Had to replace around 7 pieces around 3lbs a piece and replacong it with some new. Cured already from my local fish store will my tank be ok? I have fish and coral in it.
How large is the tank? Or better yet, what percentage of your total rock volume is that 21lbs you replaced? Either way, it shouldn't be too big a deal provided the new rock is good high quality/cured with bacteria and clean. But...you are still changing the bacteria profile of the tank in some way, so just keep an eye on things and maybe even check for any mini-cycles now and then.