I have several small size clay rocks from a stream on our farm down south and was wanting to use them in an up and coming tank, they were once solid but now, since drying, are starting to crumble. Which is the best use and how does clay affect pH and other water parameters?? Best to leave it as a solid rock or mash it up and using it as a base substrate but then read that clay makes a "unsuitable" substrate so am very unsure as how to best work with the medium. Have not yet found any details on clay and pH. All helpful advise on the matter would be great. Cheers.