I use it in all my tanks except for my 20l. Funny thing is that only my 20l has perfect water conditions. Maybe because it has 2 pounds of live rock and 2 snowflake moray eels and a hermit crab but Ive heard that the eels are a major bio load on the tank. My nano is a 15 gallon cube that I have been struggling with for a while now and It has a nice filter that was made for a 55 gallon tank so I dont know what the problem is with that. I also have a 30 gallon tank that I have a canister filter on and the water in that seems to be getting better. Can the cause of the bad water be because of my mistakes? Maybe but I find it funny that the tank that I set up 2 weeks ago with tap water and oceanic salt mix is doing the best out of all my tanks and all i have