Help With Ph

[shaunza2010]

I have been doin my water test and everthings reading fine apart from my ph which i would like to get up a bit to 7.0, 7.2
I have the CO2 natural plant system that say that will bring down the ph, I bought the chemical ph up but I am just wondering what type of rock or stone can i add that will look natural in there too and save me adding this chemical all the time

 

[Miss Wiggle]

http/www.fishforums.net/index.php?showtopic=55806

good stuff about rocks there, the one that springs to mind is limestone, not read the whole topic though sure there's more informative stuff in there