Number of fish.

That is a tough question actually. Some people will say "x inches of fish per gallon" but five 1" fish does not equal one 5" fish.


Plus you need to factor in how big the fish get. You can't put in 9 tiny hippo tangs and expect them to survive in that tank (even if they didn't fight and the filtration could keep up) because they get too large.


So now that I haven't helped you at all, what kinds of fish do you want to keep?


There is also a great thread over at R.C. where you can give your "wish list" of fish and your tank size and get professional and scientific answers about what will work from a fish compatability aspect as well as how much is too much for a 125g tank.


The people that respond are considered to be "experts in the field" and while some people around here will tell you that you can do something different because it worked or is currently working for them, a response in the R.C. topic will be for long term success. You can always make your own personal choices to "modify" the advice given of course, but it is pretty solid.




http://reefcentral.com/forums/showthread.php?t=2068112

 

Very hard question, and no unique answer.

Really it all depends on flow & filtration. If you have really good flow, and really good filtration, I wouldnt be afraid to put 20+ fish in a 125, as long as they were all compatible.

 

I have 4 tangs, 2 clowns, 2 mandarins, 2 scooters, 2 sailfin blennies, and 2 diamond gobies in mine and still have room but prob won't add anything else. I have a 125 and test my phosphates and nitrates and both are at 0. Some tangs don't get along but I've never had an issue with them fighting. Do your research to know what fish to add first. Know if you add some fish they might beat the hell out of new ones when you get them. Example Damsels! Clowns can be mean also. Know what you want to add because it can suck having to remove them.