My test kit arrive today (API) to test my water for KH & GH.
My KH is 6 which I understand is 106.8 ppm. However, I was totally shocked at my GH levels.
23 drops later and if i am doing it right is 409.4 ppm.
Just to add a bit of accuracy data on the API GH side of this discussion, I just got a fresh set of those two kits. When using RODI water + Remineralize in a bucket, the GH seems to like to go from nothing to 15 or more as I increase the hardness of the water, and I'm having a really hard time getting readings inbetween. Also on a sample of water that was reading extremely high at 40dGH (a reading that was already improbable but the color change did stick solidly...), doing a 50% mixture of that water with fresh RODI wit TDS of 0 did not give me around 20dGH as I expected but instead gave me more like 35. So...I'm not thrilled with the performance of the API GH kit although I don't know why it would be problematic (settled or unevenly mixing of the reagent in the bottle maybe?? I don't know what the reagent is so no idea if that could happen). The KH one seems fine on prepared mixtures of RODI and baking soda and reads pretty close to expected.