How do you remove a sand substrate from a tank, which contains fish, without stirring things up? One of the simplest ways is to use a gravity siphon.
When I do water changes, I remove water with a 5/8″ ID hose with pex pipe on one end (the photo above looks different because it’s a larger bucket, a larger siphon hose, and a larger pump). I run the drain end of the hose through a hole in a bucket. The bucket sits inside a plastic tub. However, the bucket has multiple holes drilled into the top (if you look closely, you can see the holes drilled into to the top of the bucket. They are just like the hole the siphon hose is threaded through.). As water fills the bucket, it eventually runs through the holes into plastic tub. Inside the tub is a submersible pump attached to a Python hose, which pumps the water to a sink.
The original purpose of this set up was threefold. 1) Water pressure in my basement where my tanks are is low because of smaller copper piping than throughout the rest of the house. This makes using a standard Python hose difficult because there isn’t enough suction to adequately vacuum. 2) Running the tap to create any useable suction wastes a lot of water. 3) I have fry in multiple tanks, so using the bucket method protects any fry that I accidentally vacuum up. The fry will go into the bucket, settle at the bottom and thus won’t flow out through the holes with the water as it exits the top of the bucket. An added bonus of the holes in the top of the bucket, if drilled to a size just below the OD of the hose, is that the hose will not come out of the bucket. This way you don’t have to worry about the hose coming out when you aren’t looking, flooding your floor.
Because of the size of the siphon hose, coupled with its short length, the gravity pull is strong and easily powerful enough to pull sand. One advantage to this is that by siphoning the sand, very little is stirred up as normally happens when using some kind of scoop. The other advantage is that, by draining the sand into the bucket, the sand is easily removed and disposed of.
I have one 75g tank with 1.5-2″ of aragonite sand. I’m replacing the aragonite with pool sand. Yesterday during my normal water change, I removed about 1/3 of the aragonite using this method in less than 10 minutes. There was zero cloudiness. This tank does not contain any fry, so I did not have to worry about accidentally vacuuming any up and into the bucket.