Getting ready to start up my new 75 gallon tank. My question is, since I will only be starting with a couple green chromis in the tank can I start with only about 10lbs of live rock? Then add more LR with the other fish that will be going in. The live rock is from a tank that I have had running for several months now. Also I plan on having 5 chromis. Can I add two then 3 or whatever, will they still school together?