All the test kits I've seen only measure chlorine up to 5ppm max. How do you measure higher levels, to be sure you are shocking correctly? I've seen the threshold for shocking listed at 8ppm, 10 ppm, and 15 ppm.
I'm currently using an HTH6-way test kit. Thanks.
You can get an estimate by dilution of your pool water sample. This will result in some inaccuracy. Take a measured amount of pool water and add an equal measure of distilled water, multiply the read result by 2, to measure chlorine up to 10 ppm. Add two parts distilled water to one part pool water and multiply by 3 to read to 15 ppm.
The better way is to get a FAS-DPD test that can measure up to 50 ppm to 0.5 ppm accuracy. You add a measured amount of water to a vial, then some powder, mix, then add another reagent drop by drop. The number of drops x 0.5 is the FC level. This is part of the TF100 kit that I use, but the FAS-DPD test is available separately. Visit http://www.tftestkits.net to see whether you want a full test kit or just this part.
What sort of test kit do you have now? How old is it? What sort of pool do you have?