swimnsaveusa wrote:DPD kits are definitely the best to use, however, they sometimes require a certain technique to get any accuracy. The AquaChek 7 is the best to go with if you were to use the strips at all, as they are fairly accurate. You are correct on the CYA scale, however, as long as you are in the 30-50 range (up to 100 if you really want to be), you don't really need to be THAT accurate, and they realize that hence not giving every 10ppm increments.
FAS-DPD and DPD are not the same thing. I agree that DPD can be tricky to get accuracy since it's a color-matching exercise, but that's not the chlorine test I'm talking about. Look at the demo link I gave for the FAS-DPD chlorine test to see that there is no color-matching required. It's a "count the drops" until the sample turns from pink/red to clear test -- very easy to do even if one is color-blind and it's very accurate. Getting either the Taylor K-2006 or the TF-100 is a huge step up from test strips and even other drop-based kits. A comparison of these two kits is described here. (I also added the 7-way AquaChek Select to my previous post, but that still doesn't help.)
Because the amount of Free Chlorine (FC) needed to prevent algae is dependent on the Cyanuric Acid (CYA) level as shown in the Chlorine / CYA Chart, it is important to have the CYA be reasonably accurate. There's a big difference between 30 ppm, 60 ppm, and 100 ppm since 100 ppm requires over 3 times the FC level to prevent algae compared to 30 ppm.