there is not set rule, and most of them are garbage and should be treated as such anyway.I have seen a few different posts, saying 1 inch of fish for every 10 gallons, or two fish per 10 gallons, As of now i have: My tank is freshwater community, with relatively small fish
2- angelfish (4")
3-neon tetra (looking to get 3 more)
4-Red glow zebras (about 1" big)
5-Cory Catfish
5-Painted Tetras (about 2")
3 Black mollies
2- orange fish (dont know their names, about (2")
dont add any more neons, as they are just going to get eaten by the angels. the zebra danios are probably gonig to be eaten also.
your painted tetras are dyed, but they are probably the blue or pink albino black skirt tetras that are fed dye laced foods, whcih is not as harmful but it will still shroten the life span of the fish. dont get any more of them.
your mollies amy start to nip at the angelfish if there are not enough females in the tank. are your mollies all male, 1 male 2 females, 2 males 1 female?