With the DPD test, you add drops of two different reagents to a water sample, mix, then compare the color to those shown on the side of the test block. You are limited as to how high of a chlorine level you can read. (I think most can read up to 5ppm.)

With the FAS-DPD test, you add a scoop of powder to a water sample which turns it pink and then add drops of a different reagent until the sample turns clear, counting drops as you go. Your reading is the number of drops X 0.2 or 0.5 depending on how much of a water sample you use. You can test much higher chlorine readings with FAS-DPD up to at least 50 or more.

Hope this info helps clarify. My recommendation is to get a FAS-DPD kit -- the Taylor K-2006 is the one we suggest.