I beleive that waterbear has said that OTO method for FC/CC really doesn't work and it makes sense because the CC is usually pretty low (0.5 to 1ppm when high) so it is unlikely that you will be able to get that level of detail out of the color comparison test.

I think the FAS-DPD test is the only way to get accurate CC. You can buy that test separately on the poolsolutions site.

Peter