So been having problems with phosphate in my tank. Way to high for healthy fish. Aro ended up with pitting in head and no, its not from diet. My water peramiters are always pristine. So here is the deal... The sandstone contained phosphate. I test them in ro water today after letting them sit for a few days. I'm taking two different other types of rock i have in my tank I have in my tank down to my lfs tomorrow along with my water from the tank to see if I'm good to go!! stay away from certain types of sandstone or rock. Do your research before adding them. The reasons I used the sandstone were because of the natural Ph buffer that it has in it. I tested it with vinegar and that's one way to tell if it has chalk; which In turn is the buffer, but its also phosphate which I didn't know till now. I'm not much of a geologist but phosphate is the color of bright white quarts like coloring along with sone being brown, and black. So if you have rocks with these colors of sediment, you might want to somehow soak them in pure water and check for phosphate. If you have a phosphate problem, could be the source if its not just something dead in the tank. And make sure to have lots of filtration if you keep a scaped aquarium. I no begginner but I do learn something everyday, and for those that don't know, just some info of my experiences 
Discus buffers are comprised of phosphate additives. Something to think about if you didn't already know.
Discus buffers are comprised of phosphate additives. Something to think about if you didn't already know.
