over the years Ive come to the conclusion that its hard to keep any fish alive in these small tanks for the simple fact that they are to small. What I mean is parameters can change in a matter of hours. You can check them one hour and in the next couple of hours you will get a different reading. Why because of water evaporation,temperature control,stable salinity, ph high n lows to name a few. Plus thats to many fish in a 20glln. Ofcourse this is only my opinion but have attempted to keep one of these small tanks in the past. And there maintenance is just to intense and time consumming. IMO best of luck.