Quote Originally Posted by cbednara View Post
readings from this morning (shocked with 2 gallons of 10% LQ at dusk the night before).
FC -1.38
TC- 1.65
Pool volume of 17,500 => PF:7

2 gallons of 10% *should* have raised your FC by 12 ppm. There are 3 possibilities: your 10% bleach is actually 2 - 4% (common when bleach is stored at high temps) OR you've got something (like agae as mentioned) creating a high chlorine demand, or you are getting bogus ColorQ readings (it *is* a 'guess-strip' reader!)

Buy 18 gallons of PLAIN 6% store brand bleach from a store with high volume sales (=fresh bleach), like Walmart. Add 6 gallons EACH evening after you get the bleach, and test FC in the AM. You *should* be seeing levels of 20+ ppm in the AM. Also get a cheap OTO drops kit: at 20 ppm, OTO is very dark yellow with an orange tinge. The 2nd evening, brush the heck out of your pool. Also, add the bleach VIA the skimmer, after making sure ALL chemicals, tablets, pills, feeders, etc in the skimmer or pipeline, are removed. Adding the bleach that way will help clean your filter.

By the way, you can test the ColorQ by collecting a sample, and then testing that sample every 20 minutes for an hour. The variations between the results is reflects the minimum (not: maximum) testing error you should assume in every ColorQ result.