Join Date: Jan 2008
As GH and KH test kits work on the principle of titration, you can double the volume of water to be tested, and just keep adding drops until you see a colour change.
The result is that each drop resolves to a finer degree (i.e. each drop is now 0.5 degrees hardness, rather than a single point). Doubling the volume again would result in a resolution of 0.25 degrees, etc.