I think my 30 gallon needs some work? help?

so my friend took the goldfish, shouldve known hed use them for oscar food :/ but better than being in a small crowded tank. my las dojo loach is about to kick the bucket, hes upside down and lying there but still breathing and my ammonias through the roof at 6ppm. i plan on letting the tank re-cycle and was wondering if i could just have a single severum fish in it. i saw them at the pet store when i went to have my water tested and the gold severums were just beautiful looking. i was wondering if i could have any in my 30 gallon?