The chlorine level you need to shock your pool depends on your CYA level. In the Chlorine Thread on this forum, you will find Ben's Best Guess chart - that will give you the recommended chlorine levels based on CYA.
If you mean the FAS-DPD powder, then I believe Ben sells refills on the poolsolutions site. The FAS-DPD test will give you a free chlorine (FC) reading which is pretty accurate. If you want to measure higher than 5 ppm with the OTO test, you can dilute the pool water sample with two parts distilled water and multiply your result by 3. This will not be as accurate as the FAS-DPD test but it's better than nothing.
Peter
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