I have a 20 gallon tall tank. I have five tetras, two frogs, three Cory catfish, and one pearl gourami. I have a good amount of live plants, decent sized air stone, and a fluval 30 gallon three stage filter. The fish have been healthy and all zoom around and get along great showing no signs of anything bad. If I added one more frog or do you think that is too much? I do 25% water changes. Is it safe adding one more frog or even a fish? Thank you!