120gal mixed predatory reef tank

[trilinearmipmap]

OK here are a couple of ideas regarding the lack of reliability of kH test kits.

My Salifert kH test kit came with a reference standard to check the kH test results against. If no one in town has a reference standard to lend you, I can bring one out next time I am in town.

The other idea is to use a pH monitor (recently calibrated against known standards) to measure the pH of a sample of tank water that has been aerated outdoors for a few hours. By aerating the water sample, the concentration of CO2 in the water will be equal to the concentration in the atmosphere. Since carbonate/bicarbonate is the predominant buffer system in seawater, you can take the pH and the concentration of CO2, and calculate the kH.

By using both these methods you should be able to come to some approximation of how accurate your kH test kit is.