I hate test kits!

[pterfloth]

If you really want accurate alkalinity results then you can do what we do in the water treatment industry, use methyl purple indicator and N/50 sulfuric acid to titrate. The N/50 sulfuric acid is very dilute and harmless. Using a 50 ml sample of tank water, add 4-6 drops of methyl purple indicator and add N/50 acid until the color changes from green to purple. Every ml of acid added is 20 ppm of alkalinity, so 6.5 ml = 130 ppm alkalinity (dKH 7.3). A 4 litre container of N/50 sulfuric acid is about $82.00 from Fisher Scientific. That's good for over 600 tests!

I also use an industrial test method for calcium and magnesium. It's 100% accurate and much cheaper in the long run.

The commercial test kits are not very good and very over-priced. Like the commercial liquid calcium and magnesium additives, the mark-up is scandalous.