What kind of material will lower ph for example somebody asked how to raise ph and i told them crushed coral is there somthing that can be added to the tank like substrate or ornaments that will do this? just wondering if there is somthing like that.

pop in a pad and bang i got 7.0 please find that dr.joe
in the same water conditions.So i don't know for sure that it is a ph problem that's holding them back but i thought it would be a good thread.