I already have an established tank and I want to add more live rock as I have run out of room to put more coral, I want to know if it will cause caos in my tank.
New live rock could potentially cause an ammonia spike as it cycles and settles in your tank. My local fish store does a good job curing their live rock before they sell it, so I have had good luck using the stuff I buy right out of the store. If you don't have access to that, or just aren't sure, cure the new rock in a seperate container and make sure it's safe before you add it to your main aquarium.
_________________ Honda NSR125
As long as the rock is good and "clean" before you toss it in (no softball sized dieing sponges, etc.), you have a well established tank, and it is not a large percentage of live rock for your tank, you should be fine.
