With the K-2006 test kit, you use 7 ml of reagent for each test, so the A-size bottle of .75 oz (22 ml) is only 3 tests, but you get two such bottles in the K-2006 test kit. The C-size bottle of 2 oz (60 ml) is about 8.5 tests while the E-size bottle of 16 oz (473 ml) is 67.5 tests. Usually you don't have to test your CYA very much once it's stable, so I would say that the C-size bottle (R-0013-C) should work well and is reasonably economical.

I wouldn't get the K-2006C kit since that has C-size bottles for all reagents and you'll only use up a lot of CYA reagent initially -- the others you will use up much more slowly. Probably the one you will use up most is the FAS-DPD Titrating Reagent R-0871-A which is much more economical in the C-size, but is sensitive to light so you don't want to get too much of it. If you do tests using a 10 ml sample size to get a resolution of 0.5 ppm, then you should last through a year of testing, but if you use a 25 ml sample size to get a resolution of 0.2 ppm, then you may go through an A-size bottle in less than a year.

Richard