You've just run into one of the follies in the fishkeeping hobby. We seem to want to have "rules" rather than think. The rules often only apply when you have the same setup as the rule used. Rocks that fizz are not bad! It just takes some thought on why they fizz.
If you take any alkaline item like limestone and pour an acid on it, it may fizz. Just junior high science. The stronger the acid, the stronger the reaction. Does that make it bad? Depends on what you are doing in YOUR tank, not what the rulemaker was doing in HIS tank.
If you have acidic water and want to raise it to a higher PH, limestone or coral may be just what you want. If you have high PH water and want to use limestone, you may see no change at all. If you have neutral water and want to use the rock you have, it is a matter of knowing it MAY change your water or may not. If you put it in and monitor the PH, then you will know what it is doing. All the other is theory which may or may not work in your tank and the way you operate. If you want African cichlids, you will like the results. If you want soft water fish, you may not.
Last edited by PlantedRich; 07-04-2012 at 02:02 PM.