I found a piece of hard coral laying outside my house. It is very light weight and has a lot of small holes. Could this coral piece become a good mount for mini phals and Neos?
Probably not. The calcium carbonate from which the coral is made may increase the TDS of water running off the rock and onto the roots. If this coral rock is fr a nearby beach, it could contain high sodium chloride as well.
If it has been away from salt water for a long time, might be OK for lithophytes that can grow on limestone.