In interpersonal relationships and diplomatic situations, subtlety is a good thing.  When it comes to test kits, subtlety is not good.

I have no complaints over the KH test.  The color change from blue to yellow is quite dramatic and easy to discern.  Fill the delicate glass tube to the indicated marker with the sample water.  Start adding the reagent from the bottle marked for KH.  The first drop will color the water and turn a blue color.  From that point, you keep adding more drops, one at a time, until the solution in the tube turns to yellow.  The number of drops required to change the color will indicate the KH, or carbonate hardness, of the sample.  Multiply the number by 17.9 to arrive at the measurement in ppm.

The GH test, however,is rather subtle.  Follow the same procedure as above, using the GH reagent.  The number of drops required to change the color of the sample from orange to green is the reading for GH, or general hardness.  It will be given in dGH, however, multiply by 17.9 to convert the reading to ppm.  The change from orange to green can be subtle.

I have several other test kits from this brand:  Ammonia, Nitrate, PH, PH high range, and this one.  The one thing they have in common, that I can fault them all for, is that the glass vials are made out of very thin glass.  They break easily.  At this point, I have more tests than glass vials.  I just have to rinse them out in distilled water and reuse the same vial for numerous tests.

I started using this line back when they were branded Aquarium Pharmaceuticals.  Some of the tests are better than others.  Meaning, the results are easy to discern.  Some are not so good.  The Ammonia and Nitrate tests are fairly easy to read.  The high range PH can be tricky.  To compensate, I have an electronic PH meter from Hanna Instruments.  Between the two, I feel confident that my PH readings are accurate.

These are widely available and fairly inexpensive.  They are not as easy to use as the test strips.  However, these have a wider range than the typical test strip kits that are available in the hobby.  If your tap water parameters are on the extreme end, say very high GH, KH, and PH, then those test strips may not give you the range that you need.  For example, if your tap water PH is 8.4, you will need a test kit capable of reading that high, like this one, or an electronic tester.  The electronic testers are expensive and have to be calibrated with special solutions.  So, for most, it would not be a good choice.  That leaves you with this brand's test kits.  They are far from perfect, but they are perfectly adequate for the hobbyist.  API should, at the very least, re-design the glass vials and make them out of a less fragile material.
In interpersonal relationships and diplomatic situations, subtlety is a good thing. When it comes to test kits, subtlety is not good. I have no complaints over the KH test. The color change from blue to yellow is quite dramatic and easy to discern. Fill the delicate glass tube to the indicated marker with the sample water. Start adding the reagent from the bottle marked for KH. The first drop will color the water and turn a blue color. From that point, you keep adding more drops, one at a time, until the solution in the tube turns to yellow. The number of drops required to change the color will indicate the KH, or carbonate hardness, of the sample. Multiply the number by 17. 9 to arrive at the measurement in ppm. The GH test, however,is rather subtle. Follow the same procedure as above, using the GH reagent. The number of drops required to change the color of the sample from orange to green is the reading for GH, or general hardness. It will be given in dGH, however, multiply by 17. 9 to convert the reading to ppm. The change from orange to green can be subtle. I have several other test kits from this brand:  Ammonia, Nitrate, PH, PH high range, and this one. The one thing they have in common, that I can fault them all for, is that the glass vials are made out of very thin glass. They break easily. At this point, I have more tests than glass vials. I just have to rinse them out in distilled water and reuse the same vial for numerous tests. I started using this line back when they were branded Aquarium Pharmaceuticals. Some of the tests are better than others. Meaning, the results are easy to discern. Some are not so good. The Ammonia and Nitrate tests are fairly easy to read. The high range PH can be tricky. To compensate, I have an electronic PH meter from Hanna Instruments. Between the two, I feel confident that my PH readings are accurate. These are widely available and fairly inexpensive. They are not as easy to use as the test strips. However, these have a wider range than the typical test strip kits that are available in the hobby. If your tap water parameters are on the extreme end, say very high GH, KH, and PH, then those test strips may not give you the range that you need. For example, if your tap water PH is 8. 4, you will need a test kit capable of reading that high, like this one, or an electronic tester. The electronic testers are expensive and have to be calibrated with special solutions. So, for most, it would not be a good choice. That leaves you with this brand's test kits. They are far from perfect, but they are perfectly adequate for the hobbyist. API should, at the very least, re-design the glass vials and make them out of a less fragile material.