Testing Shock levels of FC (FAS-DPD) uses a lot of Reagent. Even if you are testing 10mL 0.5 ppm, that's 40 or more drops for 20+ ppm. I am wondering if my math below is correct and if this should work. Going to smaller sample sizes is more intuitive half the sample size = twice the ppm. I wanted to check that against the 2 know values we had, and came up with this formula ppm = 0.5ppm/(x mL/10ml). Plugging in 25mL for x does get you 0.2ppm, so it looks like the formula works. I shocked my Spa to what I thought should be 30ppm and tested using 2.5mL and got 16 drops (32ppm) so it might not be super accurate but it will save you some reagent when testing shock levels. I don't want to waste 64 drops of reagent to check my findings. Maybe I will order an extra bottle of reagent just to test this.
mL's of water
Drop = x ppm 2.5 mL 2 5 mL 1 10 mL 0.5 15 mL 0.33 20 mL 0.25 25 mL 0.2 30 mL 0.17 40 ml 0.13 50 mL 0.1