I think it's a common thing for stores to say that, I bought an established tank from a new aquarist, it had fish and a magnificent nem, and fish. I removed it as soon as I got it home, and got it to someone with a more established tank, the aquamaxx fits my jbj 29 just fine, only thing removed was part of the tubing for the out flow on it, just one of the joints pulled and was a perfect fit, as to what first, I see a lot add fish first, after it's been established for several months to a year then add coral, I've read others add all together in a timely manner, and some who have added coral then fish.