When I needed to test water GH I used the API test kit. I found it cumbersome because after each drop of solution you needed to cap the test tube and give it to shake. The German company, Sera makes a GH test kit with a very wide test tube. After each drop of solution into the test tube, you do not need to cap it, you just give it a few flicks with the finger to disperse and thoroughly mix the reagent with your water. Very easy.