Help interpreting FAS-DPD FC/CC test results **Sorry, long, techy post**

The CC is a byproduct of the FC oxidizing the (presumptively) ammonia in your pool. It's always an indication that there's something in the pool that's being oxidized by the chlorine.

The goal of shocking is to get rid of stuff in your water that doesn't belong there. When you can hold (less than 1 ppm loss) FC overnight (no loss to sunlight) and measure nearly no (0.5ppm or less) CC for two nights in a row, you'll have have finished shocking (gotten rid of unwanted pool stuff).

Hi All;

I've seen some things that make me suspect that, with the DPD-FAS test, you will see a CC residual, when the FC gets high enough, even though there may be no actual CC's present. It's something that needs to be tested, first with distilled water at FC=50 ppm and then with distilled water + 20 ppm CYA at 50 ppm FC.