OASE BioMaster Thermo 350 canister review

OASE BioMaster Thermo 350 external canister filter. Image from https://us.oase-livingwater.com/.

Back in October, I posted about having the opportunity to review the new OASE BioMaster Thermo 350 external canister filter. I finally got around to getting that completed.

Let me start by thanking OASE Living Water for donating this canister! What follows is my honest and unbiased review of the filter components and setting it up. If I didn’t like something, I’ll say so. Likewise, if I liked something, I’ll say so.

This is not a review of the canister following extensive usage. In fact, I only ran it about 25 minutes total. If you want a review of this canister after it’s been in use, on a populated tank for an extended period, check out Zenzo’s review at Tazawa Tanks.

Unboxing and Instructions

All components were neatly boxed. Opening the filter box and removing the top cardboard support insert revealed the canister body and a separate box of canister parts (Figure 1). This separate box contains all of the printed material and attachable filter components not already attached to the canister, which consists of the following (see Figure 2):

Canister instruction manual
Heater instruction booklet
An OASE contact card / registration reminder
Warranty booklet
Action item guide (will explain more below)
• 13′ smoke grey, semi-transparent rubber hose at 3/4″ OD, 5/8″ ID
• 1 grey/clear intake extension tube (plastic)
• 2 grey/clear spray bar tubes (plastic)
• Heater dummy holding ring
• 3” piece of smoke grey, semi-transparent tubing connector (connects the two spray bars if you choose to use both)
• A bag of rubber feet for the underside of the canister body
• A bag containing intake/outflow parts (e.g., suction cups, adjustable hose adapters)
• A bag containing mounting bracket and suction cups for heater (if you choose to use the heater externally)

See Figure 3 for the bulleted parts above separated from the box.

Figure 1. Opened box of BioMaster Thermo 350. Note the parts box beside the canister. 


Figure 2. Parts box, opened.


Figure 3. Components removed from parts box.

After unpacking the parts box, I opened the instruction manual to review the parts list and ensure everything was in the box. In the instruction manual, the parts list is on page 12 and has two sections – List A and List B (parts illustration on page 2).

The second page of the instruction manual shows two figures (labeled Figure A and Figure B) with diagrams of all parts listed in Lists A and B on page 12, and each part is numbered in those two figures. However, the figures do include the part names. You have to go to the parts listing on page 12 to match the part number with the part name. Further making the instruction manual less user friendly is that the items on page 12 are misnumbered. In fact, there are 13 items in Figure B on page 2, but when you look at the corresponding List B on page 12, what should be part number 3 has no number and part number 4 is listed as part 3 (thus every part beginning with 3 is misnumbered and therefore mislabeled). I loathe instruction manuals that separate descriptive names/text from images. These should always be together.

The misnumbering error is not as big a deal to those familiar with the typical components of a canister filter. However, if you are new to canisters, you should use a pencil or pen and renumber the items on page 12 beginning after part #2. Otherwise, you will get confused as you attempt to follow the instructions.

Once I deciphered the part number and name listings, I concluded that all parts listed were present and accounted for. The next step was to remove the canister from the box and inspect it.

Manufactured in Italy, the OASE BioMaster Thermo 350, which is the middle line of the BioMaster Thermo series, is quite large (see Figure 5). It is a square canister standing ~17” tall, with the carry handle down. It is ~9 wide and weighs 10 lbs (without water). The Thermo series is named such because it comes with an integrated, removable heater. The BioMaster Thermo 350 is recommended for 90 gallon tanks. OASE states that both the heater and canister filter are UL-certified. More about the integrated heater in the Heater section below.

Out of the box, the first thing noticeable about the canister, besides its size, is the two-colors OASE uses. The main canister body and unit head (see Unit Head section) are a dark grey but many other components are a steel blue color. According to OASE, the blue colored components are items that users are expected to handle in some capacity, either open/close, turn, push, or pull. In other words, besides the grey carry handle to lift the canister, OASE recommends that you generally not try to open, remove, or adjust anything that is not blue. This is a nice feature, especially for aquarists new to canister filters. However, the carry handle itself on the unit head is not blue, which is strange. Same with the hose connection unit, discussed below after the Heater section.

Looking down on the canister from above, you’ll easily notice five key components on the unit head – the heater, the prefilter unit, the hose connection unit, locking levers, and the carry handle (see Figure 4).

Some of OASE’s component names are not very intuitive. For example, the two u-shaped, hard plastic hose connection tubes that sit on the tank rim and connect to the intake and outflow hoses are both called “hose adapters” and are identical (see Figure 15). Also, there are five suction cups and accompanying u-brackets included for holding the plastic intake and outflow tubes in place on the tank. The suction cups are called just that. But the u-brackets that fit onto the suction cups are called “terminals” (see Figure 18).

In the parts list at the top, I mentioned an Action Item Guide. This one page, color handout contains numerous photos identified by a letter. Below the photos on this guide are captions that explain each photo. These captions are labeled alphabetically and are ordered just as the photos are.  The Guide is more or less a component installation/removal guide and is designed to tell the user what each blue part does. Remember, blue colored components on the canister are designed for user contact. The Action Item Guide is a welcome informational component, especially given the parts listing error(s) in the instruction manual.

Figure 4. Top view of canister.


Figure 5. Side view of canister. Note the blue locking nuts on the intake and outflow nozzles. These do not come already installed. Also note the carry handle in the up position.

Looking at the canister from the side (Figure 5), the large blue colored latches (called fasteners by OASE) seal the unit head to the canister body. To review the components, I’ll start with the integrated heater (Figure 6, see where the heater is located in the unit head in Figure 4).


The integrated heater is a great feature because it allows you to hide the heater within the canister.

You do not have to use the integrated heater, nor do you even have to use it inside the canister if you choose not to. A nice touch is that OASE anticipated some users might not want to use the heater inside the canister. As such, they provided a mounting bracket and suction cups for placing the heater directly inside the aquarium. Also, OASE includes a “blind plug” to seal the heater chamber if you choose not to use the included heater in the canister. However, if you don’t intend to use the integrated heater at all, you should consider the BioMaster 350, which is the same filter without an integrated heater.

This is the only external canister filter I am aware of that includes an integrated heater. There are several manufacturers of inline heaters, which are intended to reside between the canister and the aquarium, but I am unaware of another canister filter with heater integration within the canister itself.

Unfortunately, the heater chamber within the canister is designed specifically for OASE heaters. Thus, you cannot use just any brand of heater within the heater chamber. However, a positive is that the OASE heaters are sold separately, so if yours fails, you only have to replace the heater rather than the entire canister.

Removing the heater is straightforward. There is a steel blue holding ring (see Figure 6) that the heater goes through. This ring is threaded on the outside so that it “screws” into the top of the threaded heater chamber in the unit head.

Figure 6. Heater outside of canister.

To remove the heater, you simply turn the blue holder ring counter clockwise. Once it’s been turned about 1/3 of the way, the heater will “release” from the heater chamber within the canister. Then you just lift the heater out of the canister. The holding ring has a small protruding plastic tab attached, which aligns perfectly with the heater’s power cord. This is important because the outside of the canister body has a small channel for the power cord to go through so that when the canister’s carry handle is closed down, it does not crimp the cord. When you remove the canister from the box, the heater is already seated inside the canister and the holding ring is in the “closed” position.

The heater that comes with the BioMaster Thermo 350 is 200 watts. Though integrated into the canister, the top of the heater is accessible where the temperature can easily be adjusted. The adjustment knob sits atop the heater (see Figure 13) and there is a small temperature setting window viewable just below the temperature a knob, allowing you to adjust the temperature while the canister is running. Unfortunately, the “on” light, which illuminates when the heating element, located on the body of the heater, is on. This light is below the heaters blue holding ring, which means it is inside the canister. Therefore, there is no way to visually see if the heater is on while it is seated within the canister. This is a design flaw, in my opinion. Either the OASE heaters should be modified so the light is visible on the top or the canister body should have a clear window to the heating chamber to view the heater’s light when it is illuminated. I would vote for the latter because some people may prefer to use the heater outside the canister. Furthermore, the heaters are sold separately so you can use an OASE heater in your aquarium without an OASE filter.

In my opinion, a 200-watt heater is generally not sufficient for large tanks (> 50g). As I previously stated, this filter is recommended for 90g tanks. Depending on both the ambient temperature of the room where you plan to use this heater and the ideal temperature for the fish you’re keeping, 200 watts may be too low. Also, if you use the heater in the canister and the heater fails (i.e., does not come on), your tank water will not be heated. For large tanks, I use at least two heaters anyway. If you do use this heater as intended (within the canister) and you’re heating a large volume of water (e.g., large tank), I would recommend adding a second heater inside the tank or use multiple BioMaster Thermo filters (more on this redundancy in the summary section at the bottom).

Hose Connection Unit

The next step was to remove the hose connection unit (see Figure 4). This is where the intake and outflow hoses connect to the canister. There is a locking lever on the canister directly in front of and underneath the hose connection unit that slides to the right in order to unlock the unit (see Figures 4 and 5). When the lever is in the unlock position, the valve that shuts off water flow into and out of the canister is closed. The entire hose connection unit can then be removed without fear of water draining out of the hoses.

Both intake and outflow nozzles that reside atop the connection unit will rotate 360 degrees, which provides flexibility when attaching and running the intake and outflow hoses to the tank. Neither these nozzles nor the hose connection unit itself are colored blue, which indicates OASE does not expect users to handle them. That’s puzzling.

The hose connection unit is similar to other canisters in that neither the intake nor outflow connections can be removed independently. They are part of one unit that disconnects from the canister, thus you can’t disconnect one flow unit (intake or outflow) independently unless you decide to remove its hose from the hose adpater.

The pump unit head, simply called the unit head, can be removed without removing the hose connection unit. Of course, when you decide to clean the interior of the canister, you’ll want to clean the underside of this unit. Furthermore, if your canister resides under your tank within a tank stand, you’ll want to remove the entire canister from under the stand to performa any kind of maintenance. That is impossible to do if you don’t disconnect the hose connection unit UNLESS you decide to remove the entire unit head. I don’t believe OASE expects you to remove the entire unit head and leave it hanging under the tank when you remove the canister to perform maintenance, so not coloring the hose connection unit blue must be an oversight, in my opinion.

Prefilter Unit

This is an interesting component of the Biomaster canister. It’s basically a long spray bar tube inside a plastic sleeve (see Figure 7) within the canister. The spray bar inside the plastic sleeve holds multiple cylindrical, foam carbon sponges, which slide over the spray bar (see Figure 7). This is all mechanical filtration, filtering water before it ever gets to the media trays. The plastic sleeve simply slides over the sponges that surround the spray bar. Water flows from the filter intake on the top of the filter straight into this sleeve, through the sponges, in through the spray bar, then up. Water then exits near the top of the unit and into the main canister well where the media trays reside. These prefilter sponges capture all but the smallest particles in the tank water before the water gets to the media trays.

Most canisters come with foam sponges in the media trays (either the bottom or top trays depending on the filter brand), which are designed to prefilter the water before it contacts the bio media. Many aquarists also prefilter their filters by inserting cylindrical sponges over the water intake inside the tank. OASE takes a different approach here by using a whole separate chamber within the canister for water prefiltering and utilizes special carbon infused cylindrical sponges. This chamber actually holds a large volume of water (.5 gallons). Most other canister filters intend for the user to dedicate at least one media tray for mechanical filtration via a sponge. Not sure what kind of advantage this provides or even if it does. I’ll test that out once I have the canister running for some length of time.

The size of the Biomaster canister determines the number of cylindrical sponges that come pre-installed on the plastic intake tube. This canister (350) comes with five sponges. The 250 comes with four and the 600 comes with six.

Three different densities of replaceable prefilter sponges are available from OASE for the prefilter unit. The sponges that come with the 350 are medium density and are rated 45 ppi (pores per inch).

To remove the prefilter unit, you must first make sure the locking lever is in the unlock position. NOTE: Removing the prefilter unit, by itself, from the canister can only be done when the hose connection unit is also in the unlock position. However, you can remove the prefilter unit from the canister without unlocking it by removing the entire unit head. The prefilter unit will remain attached to the unit head this way.

Figure 7. Prefilter unit with plastic sleeve and stacked foam sponges.

The five cylindrical sponges are easy to remove (for cleaning or replacing) from the long spray bar intake tube as they stack (see Figures 7 and 8) on top of each other. The downside to this is, if you remove the prefilter unit and notice that the top sponge is really the only one of the five that needs cleaning, you’ll have to remove the other four first to remove it. However, I believe that scenario is highly unlikely.

Figure 8. Prefilter unit with sleeve removed and the five foam sponges removed.

As I stated previously, the round, blue top of the prefilter unit is actually a pump. The instructions say it is for expelling air from the canister. Depressing (or pumping) this blue top repeatedly will pull water from via the intake from the tank and into the canister allowing it to fill. In effect, it is a priming pump. While it is expelling air, it is simultaneously pulling water into the canister from the tank.  Since the blue pump is part of the prefilter unit, I call the whole thing the prefilter/priming unit. OASE calls the blue pump a “suction button,” which again is not very intuitive.

It should be noted that the prefilter unit does separate near the top. Thus the top piece housing the blue pump (or suction button) separates from the bottom piece connecting the vertical intake tube (what I call a spray bar). This is so you can clean any buildup where the water actually flows.

Media Trays

There are five media trays inside the 350. Four of the five trays come with sponges, which are already inserted in the trays. The fifth (and bottom) tray contains a bag of plastic bio media. Like other external canisters, the media trays stack. Every tray except the top tray has built-in handles for easy removal from the canister body (see Figure 9).

The top tray is shallower than the other four (see Figure 10), comes with a removable tray cover (see Figure 11), and contains a different colored sponge (red) than the sponges in trays 2-4 (blue).

The red sponge in the top tray is rated at 20 ppi (pores per inch) and is colored differently so you know it goes on top (remember, the top tray is shallower than the other trays). The blue sponges in trays 2-4 (see Figure 9) will sit inside the top tray if you chose to use a blue sponge there, but they are too thick to allow the top tray cover to seat inside the tray. The blue sponges are rated at 30 ppi.

As for media, you can use whatever media you choose in each tray and you can configure the trays how you want (the four equal sized trays are identical), but the top tray has to be on top and the top tray cover must be seated in the tray correctly. When the trays are installed and stacked, they form the channels for both the prefilter unit and the heater (see Figure 12).


Figure 9. Media tray showing handles.


Figure 10. Side view of top media tray (left) showing depth compared to the other four trays (right).


Figure 11. Top media tray with red sponge and removable tray cover.


Figure 12. Top view of canister with unit head removed.

Unit Head

The unit head contains the canister’s pump and impeller, which are located on the unit head’s underside. The unit head is also where the hose connection unit, the prefilter unit, the heater, and the carry handle all reside (see Figures 13 and 14). I mentioned the temperature adjustment knob in the heater section above. It is easy to see below in Figure 13.

I’ve mentioned the canister’s carry handle a few times. You can see it on the unit head photos (see Figures 4, 13, and 14). I should mention that the canister has four fasteners or latches that seal the unit head to the canister body, which you can see extended in Figure 12 above. If the canister carry handle is in the down position, as shown in Figure 13 below, the two fasteners right below where the handle attaches to the unit head can NOT be opened. This is a safety feature of the canister to prevent you from accidentally disconnecting the unit head before unlocking the hose connection unit. Note the tab on one side of the handle in Figure 14. Both sides of the carry handle where it connects to the unit head have this tab. When the handle is in the down position, as it is in Figure 14, the tabs on both sides of the handle block access to the two fastener pieces on those sides. Thus, the unit head cannot be completely fastened or unfastened unless the carry handle is in the up position. The position of the carry handle does not affect the fasteners located on the other two sides.


Figure 13. Top of unit head removed.


Figure 14. Unit head removed and on its side showing the prefilter unit, hose connection unit, and heater. NOTE: the prefilter unit, hose connection unit, and heater are still attached. These can each be removed from the unit head.

Hose Assemblies

The instruction manual guides you through connecting the hoses to the hose connection unit on the canister and to the adjustable hose adapters. What OASE calls an adjustable hose adapter is the u-shaped hose connector that straddles and sits on the rim of your tank (see Figure 15). One of these is for the canister intake and one is for the canister outflow. In many other canister brands, these connectors would be distinguishable. The two adapters with this canister are identical, and each has a built-in flow regulator (see Figure 15), which is adjustable, hence the name – adjustable hose adapter.  A hose piece will run from each of these adapters down to the canister and connect to the nozzles on the hose connection unit. Proper placement of the canister is below the level of the tank. Most people put their canisters inside their tank stand, if a stand is being used. If you aren’t using a conventional tank stand for your tank, just place the canister on the floor somewhere around the tank.

Though the flow regulators on the hose adapters are a nice feature, I found that adjusting them on both adapters (intake and outflow) didn’t result in significant increase or decrease in water flow. Flow rate changes are absolutely noticeable, but not what I would consider significant.

Figure 15. Adjustable hose adapter showing flow regulator and blue hose lock nut.

Because the rubber hose that comes with the canister is a 12′ piece, you’ll need to cut two lengths, depending on the height of your tank. I cut two pieces at 56″ for assembly and testing. Part of the assembly of the hoses involves large, blue plastic locking nuts (see Figure 15). There are four of these. Screw one nut onto the threaded parts of each adjustable hose adapter.  Then push one end of the hose over the threaded part of the hose adapter (Remember, these adapters are identical, so it doesn’t matter which hose adapter you designate as the intake hose or the outflow hose). You will then tighten the blue plastic locking nut on each adapter so that it tightens over the hose.

Next, you will need to attach the other ends of each hose over a nozzle on the hose connection unit. Make sure you have placed one of the blue plastic nuts onto each nozzle before you attempt to attach the hoses. Since the hose connection unit is removable from the canister, I would recommend that you remove it before you attempt to slide each hose over a nozzle. It’s easier to get leverage while holding the hose connection unit in one hand and a hose in the other. This is important because the hoses are quite stiff. Trying to connect the hoses to the nozzles while the hose connection unit is seated in the canister would be awkward. Once you have pushed each hose over the nozzles, screw the blue nut down over each hose to secure the hose to the nozzle.

Figure 16 below shows the hoses connected to the hose connection unit on the canister. Note the blue locking nuts securing the hoses to the nozzles on the hose connection unit.

Figure 16. Canister hooked up and running on plastic tub used for testing. Note the slack in the hoses and the fact the filter was not directly beneath the plastic test tub.

Once you have completed the hose assemblies, you are ready to run the hoses to the tank. If you still have the hose connection unit disconnected from the canister, position the adjustable hose adapters onto the back of your tank. Be sure and note which hose is the intake and which is the outflow. The nozzles are labeled on the hose connection unit. Once you have the adapters roughly positioned where you want them, attach the spray bar to the outflow adjustable adapter. Alternatively, the canister comes with a flow distributor that can be used on the outflow adjustable adapter if you don’t want to use a spray bar. The flow distributer is shown in Figure 17. If you use the spray bar(s), you can position it horizontally or vertically in your tank. Remember, the canister comes with two spray bars and you can connect them together with the included spray bar connector, if you choose. To secure the various water flow components (spray bars and intake tube) to the tank, use the included suction cups and terminals (see Figure 18). To assemble the suction cup units, insert the top of the suction cup onto the terminal base and then attach the connected unit to the desired components where appropriate on the tank.

Figure 17. Flow distributor attachment for outflow hose adapter if not using the spray bar(s).


Figure 18. Suction cup (l) and terminal (r).

Not pictured is a strainer basket that attaches to the end of intake tube inside the tank.

Canister outflow

You can see a photo of the canister all hooked up in my fish room in Figure 16 above. I used a plastic tub as a test tank and just placed the canister on the floor. To fill the canister, make sure the intake tube of the intake hose is submerged in water. Pump the priming pump atop the prefilter unit several times until water begins to flow on its own into the canister. Once the canister is full, water flow from the intake will cease. You’re now ready to start the canister’s internal pump.

The priming pump worked flawlessly for me. I didn’t count the number of times I pushed it down, but I think I probably pumped it 5 or 6 times before there was enough water flowing through the intake hose to start filling the canister with gravity. It took less than a minute for the canister to fill. Once it was full (i.e., water stops flowing in the intake hose), I plugged the canister in. It started immediately and only took 10 or 15 seconds to purge all the air. Remember, I started this process with the canister completely empty of water.

Once the canister had been running for about 5 minutes, I tested the flow rate. I ran two tests. I ran the first test with all the media trays full, as they came right out of the box. This included the five prefilter sponges stacked in the prefilter unit. I ran the second test with all of the media removed.

I conducted each test by filling a 64 ounce (.5 gallon) container with water from the canister outflow using a stopwatch. I did two timings with canister media in and four timings with media out. The two times for the media in were 12.96 and 12.97 seconds. That calculates to 138 gallons per hour.  Since I cut my hoses at 56″, there was some lag in the hoses between the top of the canister and the top of the plastic tub (see Figure 16). The height from the ground to the top of the test tub was 53″.

For the second test with all media removed, I did four timings and took the average. The times, in order, were 10.99, 11.33, 11.41, and 11.11 seconds. The average was 11.21, which equates to 162 gallons per hour, a noticeable flow increase versus the first test where all media were in. However, that flow rate still does not approach the maximum flow rate of 300 gph listed in the canister’s specifications at 5.9′ maximum head height. You can see a video of the water flow through the spray bar below (this was with all media in).

I suspect my hose lag is adding some tube friction to the head pressure, thus lowering the flow rate. If OASE’s rating is accurate, I would not expect the little bit of lag to reduce the flow rate to just above HALF of OASE’s rating. Without knowing how OASE conducted their own flow rate tests, it’s hard to say why there is such a discrepancy. Nonetheless, it’s not a problem for me. More on that in the Summary section below.

Warranty information

OASE warranties their BioMaster line of filters for 3 years, standard. If you register your filter online, they give you an extra year warranty. They call this a 3+1 warranty, which is really nice.

Summary/Overall impressions

The canister if very easy to set up and get going. All the components seem well made and solid. All latches and locks operated very smoothly and everything fit together well. There wasn’t anything about the installation that was difficult, but there are a lot of components that you don’t typically see on external canisters.

Once I started the canister, I ran it for about 10 minutes. It was extremely quiet. In fact, I couldn’t hear the filter at all, only the water flow into the plastic tub. I even put my ear down to the canister and could barely hear anything. As I mentioned above, the flow rate was not very high in either test.  For both tests, I had the adjustable flow regulators in each adjustable hose adapter opened all the way.

I did not test the heater because, well, it’s a heater. It will either heat or it won’t. However, having the ability to hide the heater in the canister rather than inside the tank is nice. Remember, if you rely solely on the integrated heater to heat your aquarium and the canister stops working, your tank water will not be heated. Once I install the filter on a tank and begin using it, I’ll plug the heater in and see how long it takes to heat the tank. That’s a post for another day.

Other than the disappointing flow rate, the canister is solid. I love how quiet it is. Like I mentioned previously, it has five media trays – a shallow top tray and four lower trays. The specifications claim the canister has 1.5 gallons of filter volume with .5 gallon of prefilter volume. It’s a big canister. The media trays will hold a large amount of media. Five trays also allows for multiple configurations, depending on how you choose to use the canister. I would have preferred the canister come with more bio media than the one bag. Since the canister has a separate prefilter chamber, it seems OASE could have provided more bio media rather than sponges for four of the trays. Yes, many people use sponges for bio media, but including additional non-sponge media would be nice.

A word of caution when you remove the prefilter unit or heater from inside the canister when the canister is full of water, such as for cleaning or replacement. When you insert the component back into the canister, don’t do it quickly. Water will be displaced too fast, resulting in some of the water shooting up out of the component’s chamber.

OASE offers a full line of replacement parts, including additional foam sponges at various ppi. In fact, you can purchase a whole new unit head (minus the heater, hose connection unit, and prefilter unit), but it will set you back $110, at present.

My long-term concerns are that the canister has multiple points of potential seal failure. Unlike most canisters that seal in two places, the pump head unit itself and hose connection unit, this canister has four – 1) the removable prefilter unit, 2) the removable heater, 3) the removable hose connection unit, and 4) the unit head itself. That means there are four separate places on this canister that could conceivably leak.

Also, because there are so many removable external components, there is a learning curve for understanding the order in which some things have to be unlatched or unlocked before components can be removed. Because of that, this canister may not be the best choice for novice aquarists or aquarists new to canister filters.


  • Very quiet
  • Easy to prime
  • Separate, removable prefilter unit
  • Integrated, removable heater
  • Only external canister on the market with an integrated heater
  • Large media trays
  • Sturdy carry handle
  • Lengthy input/output hose
  • 360° rotatable hose connection nozzles
  • Flow controllable hose adapters
  • Mounting components for using the heater external to the filter
  • Parts engineered smoothly, solidly built
  • Nice Action Item Guide describing the blue colored components
  • Warranty


  • Not all components meant to be handled are colored blue
  • Multiple, potential points of seal failure
  • User manual errors
  • Non-intuitive component names
  • Lower flow rate than claimed (Note: Without knowing how OASE measured that rate, impossible to attempt to replicate)
  • New to the US market, so long term dependability is unknown. NOTE: Thanks to one of the readers who pointed out an error here. I originally said it was new to market. I’ve added “US” to the bullet to make it clearer.
  • Small amount of plastic bio media included
  • With so many removable components, knowing the order of things to be unlocked/moved before a component can be removed is non-trivial

I would definitely recommend this canister with the caveat that I have not tested its dependability. Though the low flow rate might bother some users, it doesn’t bother me. I tend to use two canisters on all of my larger tanks anyway. Furthermore, having more than ample media capacity makes up for the lower flow rate, in my opinion. Nonetheless, my view is that the pros for this canister far outweigh the cons.



12 thoughts on “OASE BioMaster Thermo 350 canister review”

    • Hi Ben. Thanks for the note. While the word “new” is subjective, I should have made that comment clearer. What I should have said is that the canister is new to the US market. When OASE re-entered the US market in 2014, they introduced some new products but the Biomaster line was not one of them. I believe the Biomaster Thermo hit US shelves in early 2019. Not sure where you are, but maybe it’s been available longer where you’re from. I think it was in Europe as early as 2016.

      I fixed that bullet in the post to make it clear that I’m referring to the US market.

      I hope you enjoy the blog and thanks again for the note.

  1. Thorough review and having used this same model for 7 months now I can agree with most of ypur comments. I really like the pre-filter and integral heater. I also agree on the wattaage vs tank size. For my usage I don’t have a problem as my 50 gallon saltwater tank as the tank runs warm. I live in Florida and run central air so only in the short winters does the heater become a factor.

    I do agree with your comment about the indicator light i.e. it would be nice to see it operating. But that being said, I have had too many heater problems especially when the heater fails and cooks the tank. So I have the Oase heater on an Inkbird controller.

    As I mentioned, I use this on a 50 gallon saltwater tank. I don’t have room for the traditional sump under the stand so I use this filter as well as a hang on the back AquaMaxx protein skimmer.

    I only keep have one tray of media (Bio Home Ultimate) in the filter and don’t use any foam in the other trays. The rock work and gravel in the tank provide enough surface are for the beneficial bacteria. In the trays, I use depending on the need a combination of Chemi Pure Blue, Phosguard, Carbon, or Purigen in the trays.

    I also run the output of the filter through a 25 watt UV sterilizer. The water is the tank is crystal clear. The intake for the filter is from a drilled overflow box where the overflows are about 3 inches from the surface. The lines coming off the overflow box are hard piped until 2 feet before the filter body and have inline gate valves to control flow. My concern initially was having too powerful a pump but as your testing indicated it isn’t as strong as advertised. So the valves stay fully open.

    I have made the usual mistakes when first using the filter e.g. forgetting to ensure the pre-filter stage was correctly locked down before opening the lines. This is where those gate valves came in handy. I also quickly learned to slide the pre-filter in slowly. Also when I take the top off for maintenance I always pull out the impeller and clean the magnet surface. The filter started to make a clicking sound and I found the impeller magnet surface has an algae build up. Its very easy to remove the impeller.

    Again thanks for a very thorough and honest review. The integral heater, prefilter and quietness make this a keeper for me.

    • Hey Robert!

      Thanks for the comment. Sounds like you’ve got a good set-up going. I have to admit I have still yet to install the BioMaster on any of my tanks. I had planned to use it on my 55g, but if you follow the blog you’ll know that tank blew a seal and I replaced it with a 33g long (same footprint). I’m glad to hear from someone who has the filter in use, though. I have a new plan for mine, but it will be a few months. Oase has a really good reputation. Thanks for reading and please tell your friends about the blog!!

  2. Wondering if you can help. I’ve been using the biomaster 250 for a couple of weeks now. The air flow seems to of slowed right down coming in to the tank. What can I do?

        • Hello Ashton. Thanks for the note. Which issue are you asking about? A water output problem or something else? Glad to help if I can. If you’re wondering about the water flow, see my reply to Russel’s comment below.

  3. I just bought one and live it. Only problem is that I cant seem to figure out which way the water travels through the media. Which basket is “first”?

    • Hi Russel. Thanks for the note and for reading. Water travels through the cylindrical stacked sponges first and then up from the bottom of the canister. So the “first” filter tray will be your bottom tray. In other words, water is pulled from the bottom of the canister up through the stacked trays and exits the canister at the top. Since the cylindrical sponges that cover the long plastic tube act as prefilters, you can arrange your media in the trays any way you want. OASE has bio-media in the bottom tray and foam sponges with varying densities in the upper trays. If you remove the cylindrical sponges and prefer not to use them as prefilters, then I would probably put foam sponges in the bottom couple of trays and bio-media or chemical media in the upper trays. Hope this helps!

  4. I love my filter but I started to notice the flow from the spray bar is slowing down… I cleaned everything really well… And it is getting worse. Currently only has water coming from half the bar and slow dripping from the other half. I swear I cleaned the bar as well. Do you have any ideas?

    • Hi Lauren. Thank you for visiting the blog! When you cleaned, did you also rinse out your media? Have you tried removing all of your media and then running the filter? If the water flow sans media is still low, then it sounds like a possible impeller problem. Try removing the impeller and inspecting it. You may need to clean it also. In fact, I find it’s a good idea to clean the impeller and impeller housing whenever I clean all my filters. If the flow is normal without media, try rearranging the media and see if it improves. There are really several issues that could be causing the slow down, but if you can’t see anything obvious you need to do the process of elimination. Good luck!


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