I agree with
D
deeda
big chunky rocks work the best. Free standing or stacked, the big rocks stay put, despite digging Cichlids. Years ago I incoorperated Lava Rock in a hardscape. It looked good but due to the rough surface, regularly caused abrasions on fish.
I like the look of algae covered Limestone in an African Cichlid tank.
The Limestone naturally buffers the water. Here's a pic of a Limestone rockpile in my tank. Both end pieces weigh between 40 lbs - 50 lbs apiece.
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