Ah yes you are probably right (I just used a standard 15 gallon). I think having 6 male guppies at that stocking level will cause them to be very territorial. Are there any other fish you are looking at getting? Or do the guppies need to be in this tank?
They don’t have to be in there, but many people on this forum recommended that I get all males so I didn’t overrun my tank with fry, and I do enjoy them.
