If you’ve been in the hobby for any length of time, you’ve encountered phosphates at some level or another in your tank water. If it’s not coming from your source water (the water you use to replace your tank water during water changes), then it’s coming from waste decomposition in your tank.
Phosphate is typically a greater problem for saltwater reef keepers, but can be a problem in freshwater systems. Don’t fret, though. It’s non-toxic to fish. However, you don’t want phosphate levels to get too high or you’ll be fighting a never ending battle with algae. Unless you’re keeping Mbuna cichlids from Lake Malawi, which actually feed on algae, or other heavy algae consumers, excess algae can cause all sorts of problems, which is a discussion for another day.
So how do you control phosphate levels? Actually, it’s quite easy. There are many solutions available to the aquarist. One of the most common is GFO (granular ferric oxide) media, which, as its name suggests, is a loose media that requires media bags. However, there are other types. Personally, I use Poly-Filter manufactured by Poly-Bio-Marine in Reading, PA. It resembles a scrub pad and comes in a couple of different dimensions. I use the 4″ x 8″ pads (pictured on the right, below) and cut them to fit my filters. I don’t really have a phosphate problem, per se, but Poly-Filter will also remove heavy metals, toxic ammonia, and various harmful organics. It’s more of a safety net for me than anything else.