Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Rock for Rift Lake Cichlids can be of limestone origin. If it releases minerals to the water that is exactly the right conditions for hard water fish.
If you have African Cichlids like Jewels or Kribs, that is, soft water fish, then you will need to test the rocks.
Get some small broken off pieces and test in a jar of water. Test GH, KH, pH and TDS for a week or so. If any of these values rise, then the rock is adding minerals to the water, and may not be a good choice for soft water fish.