Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Put a handful of each material in a separate jar with some tap water, and another jar that has nothing but tap water.
Test GH, KH, pH, TDS at the start, then once a day for a few days. You can carry on, tested a couple of times per week if you want to see long term small changes.
If none of these show the problem, then look at other things. Do you have any rocks in the tanks?