Originally Posted by Tom Barr

The KH reference solution you make yourself.
You use DI water and baking soda to make it very precise.

You place this solution in an air gapped container, this allows the gases to mix, but not KH, KH has no atmospheric component(at these temps anyway), whereas CO2 does.

So the CO2 can mix, but not the screwy tank water with it's tannins/non bicarb alkalinity and semi accurate KH test methods.

The pH probe adds more ACCURACY than the colormetric drop checker method and for those without good color preception eyc.

You also do not need a colormetric solution in the drop checker if you use a pH probe, just a ref KH water solution.

With a good pH probe and good accurate reference solution, you should be able to get very close.

The rate of response will be slower since the gas has to go to the the air gap and back into solution again.

But that's not too long I'd imagine.

Regards,
Tom Barr