I have a 50 gallon, Fish Only, cycled tank (established for over 2 years now), with dead/frozen coral and a few pieces of solid rock. I run a cannister filter and protein skimmer, and use crushed coral as my base. I have been toying with the idea of changing the scenery up a bit for my fish by adding different pieces of rock for stacking and creating more caves and hiding places.
However, many years ago I once introduced rocks (not sure what type, but they were very porous) to an already cycled system that completely threw my water out of cycle and killed all the fish in my tank in a matter of days. To avoid this mistake once again, what kind/type of rock should I be looking for? Are there any risks that introducing any rock could once again throw the water balances out of whack? I was thinking of buying some chunks of dry stone(?) I saw at my LFS
, which looked ideal for the new scenery I envisioned.