That rule does not apply for saltwater tanks at all. Also as the tank size inceases u can add more like take a 55g tank a pair of clowns two reef safe wrasses and thro in a blenny or a goby and ur at ur limit. Now u have a 150 you could get away with adding more then 3 times that amt of fish mass due to a more lr volume sump size more filtration. There is no def answer to the infamous "how many fish?" As long as u add your live stock at a slow pace and your levels maintain stable and everything seems happy and stress and disease free you can prb get away with adding another fish. As long as u get fish that belong in whatever size tank u have.
Sry about the ramble you just see this question so many times. And really as a tank owner only you know if your tank can handle another fish. If u see disease bad algae growth or you have been having bad luck adding additional fish don't do it but if your tank is doing well go for.
Sry about the ramble you just see this question so many times. And really as a tank owner only you know if your tank can handle another fish. If u see disease bad algae growth or you have been having bad luck adding additional fish don't do it but if your tank is doing well go for.