Any form of coral/shells, whether as sand, crushed or whole, should be viewed by beginners with caution. It is a decision to alter the basic water chemistry upward (in pH, KH, GH) possibly away from your source water. Since source water is both the starting point for maintenance water and the beginning point of emergency water, any departure of the steady tank chemistry has to be evaluated. Is some aspect of the chemistry, especially some mineral content difference, now a dangerous factor for the fish? In many cases the difference may be slight enough but often enough we find beginners who manage to get the worst of all worlds, having chemistry differences they are not aware of and dealing with only partial knowledge their fish and the biofilter and possibly trying to deal with diseases helped along by fish struggling with water chemistry situations that are tough for them.
My gut feeling from my time in the hobby is that most beginners are better off with chemistry neutral substrates, unless a thorough evaluation has been made and the plan to alter water makes sense and the work involved is accepted. I don't want to sound like an expert in this regard (OM47 is thoughtful of his own experiences and has knowledge in this area and I value his and other experience aquarists thoughts (mag123, you may have years of experience with this too, not leaving out that possibility!) also drobbyb has put measurements to some of these topics) as I am not one who has done the thing of using altered water on a steady basis, so just want to qualify my first sentence.
~~waterdrop~~
