Rock with low kh/ph ?

[Lusitanos67]

Hi,

I would like to buy rocks, for a amazonian tank, and I would that the kh and ph stay low (5<ph<6.5).
I like the style of seiryu stone, his color, etc... Can you help me to make a choice ?

Thanks

 

[5678]

I bought TGM blue stone for this purpose. Nice colour without affecting chemistry. Cheap too!