Originally Posted by LAXplaya
usually the general rule of thumb is 1 inch of fish per gallon to be safe. I have used this rule and pushed it a little bit but it is good. Remember everyone wants lots of fish but dont overcrowd it too much or they will die
This rule is wrong, and is ridiculously overcrowded. Come on, can you imagine 9 fully grown panther groupers in a 210? That would be ludicrous and insane. Inch per gallon rules do not work because they do not take into account waste load of fish, how much the fish eats, and how large the fish is.
50 inches of grouper is SIGNIFICANTLY different than 50 inches of gobies. You could have 50 neon gobies in a 210 and not really have to do more than monthly water changes. However, if you had just 2 panther groupers, you will be doing large weekly to bi-weekly water changes.
In all honesty, there is no way to tell how many fish you can put in a tank. It all depends on the fish you choose, amount of filtration, amount of live rock, how large your skimmer is, how much flow you have, and so many other things.