"The colors on the cards for some the various tests are hard to read compared to the test sample. The colors on printed cards are not accurate as compared to sample, or in some cases do not vary enough from one level to the next to determine where the sample falls. (To compare, I pulled out my swimming pool PH test kit - this has very accurate coloration and the PH can easily be read to accuracy of 0.1) The ammonia test has shades of green that look almost the same on the card making it very hard to take accurate measurements (0.25 ppm and 0.5 look the same shade of green, and then 1, 2.5. and 5 ppm all look almost the same - especially when trying to compare to the sample which is not quite the same green to begin with, no matter what the level of ammonia), though it is probably good enough to measure the extremes. KH and GH tests seem pretty accurate - they work by counting drops of reagent required to change a color from red to blue (or vice versa), so it doesn't matter if card color is a bit off.
I am now looking for a new aquarium PH test kit that is easier to read accurately.
All in all, the kit works, and gives 9 different tests, but one is probably better off buying things separate, and finding PH & ammonia that are easier to read. Fe, KH, GH, NO2 probably ok, Chlorine I didn't try (well water), nor did I try the CO2, but start & finish colors are very similar here.
PS. even though this is a test kit it comes with 2 little bottles of aquarium plant fertilizer which is really just a lead in to buy their bigger bottles, and make the kit look bigger."