So I have a 55 gal. I have about twenty or so small fish in there. Mostly corys, tetras, danios etc. I had some guppies but the other fish pretty much tore their fins off and killed them. I have a dwarf gaurami who is being treated the same way. Is it possible I will have to go with only fast, nippy fish? Also how many small fish like this can a 55 support? I have two 350 gph filters so it is filtered well. Thanks.