Adjust the water for the fish or the fish for the water...

JDM

Based on the ratio of RO water to tank water in the last change the GH and KH should be no lower than 19 in either hardness at absolute best, a little higher is more likely though. In that case a 17 and 14, respectively, indicates a fairly large natural adjustment factor of 10% or more. The RO water might produce as high as a 13% difference assuming a zero TDS content.

Jeff.