I purchased some rocks listed on a website that were supposedly "Yamaya Stones" which are inert rocks -- wouldnt effect the PH of a tank.
They were cheap, about 5 dollars, but shipping was 20, so I paid like 30 bucks all said and done.
The second I opened the package I could tell these were a MIX of different stones and I saw instantly some white veins one some.
I tested them and most of them were NOT inert, and put them in a 2 gallon tank, out of curiosity.
Within 3 or 4 hours my ph was off the charts high. I am really frustrated because this site is all about aquarium supplies. They seem to be a popular site located in Canada, called "Angelfins" and I was really surprised they couldn't send me the right ROCKS of all things, sheesh!
Make sure you double / triple check rocks before buying any!! arugh!!