ok, the general rule is 1 inch per 5 gallons of water, but a properly set up system with LR,LS and a SKIMMER, can go as far as 1 inch per 2 gallons OF WATER, remember, this is just a guide, amny things can make a difference here, obviously larger fish will affect the ratio sme, but aggressive feeders, should be given special consideration, for they make bigger messes, which your filtration needs to clean up, exceeding your tanks capacity could and probably will be very detrimental
HTH and good luck
Oh yeah, consider his advice about the trigger, when they get larger they get very aggressiv, which is cool, but, hard to give roommates, besides, they should have at least a 135(MINIMUM)gal;
and contrary to prior belief SW fish do NOT grow to fit your tank, they will grow anyhow