The Sun, Chlorine & CYA

[chem geek]

Putting the CYA into panty hose and putting that over a return (as you did) has it dissolve faster. Another alternative is to use the fast dissolving CYA from Natural Chemistry called Instant Pool Water Conditioner at this link which is a sodium salt of cyanuric acid in a slurry. Another alternative is to add Dichlor powder/granules which will add 0.9 ppm CYA for every 1 ppm FC you add and it dissolves rather quickly in the water. Since you need both chlorine and CYA (apparently), the Dichlor is a good option for you. One pound of Dichlor (dihydrate) in your 28,000 gallon pool will increase the FC by 2.4 ppm and the CYA by 2.2 ppm.

30 gallons of 6% bleach in your 28,000 gallon pool is 66 ppm FC worth. That's a lot, even over 2 days. I assume that the pool store is using a "count the drops to go from red to colorless" FAS-DPD chlorine test to check your chlorine levels. If instead they are using the 5-drops turns red DPD chlorine test, that will get bleached out at high chlorine levels above 10 ppm FC so you will really have chlorine when you think you don't.

By the way, 4 pounds of CYA in your 28,000 gallon pool should be about 17 ppm CYA. The CYA takes a while to dissolve and distribute evenly in the pool, but 17 is well below the 30 ppm in most tests so will be hard to check precisely.

If you have 17 ppm CYA in your pool right now, then I don't think that much is getting lost to sunlight -- at least not more than half of the FC level (and from what I've recently learned, probably far less than that -- at high FC levels the chlorine near the surface "shields" the chlorine below so it degrades more slowly). I think it's mostly getting consumed by algae IF the pool store test isn't getting fooled. If you have a 5-drops turns yellow OTO chlorine test, then that would be a good verification that indeed the chlorine gets fully consumed.

Richard