The limestone decorative rocks in my aquarium are shooting my pH to 8.0-8.2. I want to replace them with something inert so that I can at least bring the pH to 7.6. Is quartz inert? Will I have the same problem? I cannot pay the $2.00 or more per pound for the pet store accent rocks to fill a 240 gallon aquarium! Besides that, most of them are limestone as well. Is there a commonly used inert landscaping rock I could use? I have a variety available for $0.29 a pound.