The Sun, Chlorine & CYA

[ths49286]

Opened our 28,000 gal, sand filter, inground vinyl lined pool 2 days ago (sun.), in southern Michigan. Once we are up and running we use a SWG for chlorination. The water was green and the bottom had the usual pine needles, worms, dirt, ect. that got thru the cover over the winter. I have added about 30 gal of bleach over the past 2 days, the green is gone and the water is bluish white. I have also vacumed some of the crap off the bottom and backwahed a couple of times. I have one of Bens PS322 test kits but have not been able to get it restocked for this year so bought a cheap kit at WM and gone to the pool store for testing. I have added about 4 pds of CYA over the past 3 days and am 10 or below, added it using a stocking over one of the returns. I added Borax to get my PH to 7.4, and akalinity is at 80. After adding the bleach at night its gone during the next day, I assume from eating algae and the sunlight. Since I am having trouble getting me CYA up I was thinking of getting some of the chlorine granules with CYA and adding them. For tonight I am adding 10 more gallons of bleach. I am interested in any advice about switching to the granules. It was 80 today and the next 2 days are supposed to be sunny and in the 80's.

[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

[ths49286]

Thanks for your reply. I have a 5 drop test kit and 3 hours ago I tested 0 chlorine. I will go out tomorrow and and look for the dichlor. I expected the chlorine to get used by the algae but the loss of CYA stumped me. The water is sill quite cold, 60, but should heat up over the next few days. Also used the kit from WM to test the CYA level, only clouding the test tube water slightly. What are the ingredients of Dichlor, or does it possibly go by another name. With it heating up here I want to get this cleaned up. Thanks again!

[chem geek]

Dichlor goes under any of the following names:

Sodium dichloro-s-triazine trione
Sodium dichloroisocyanurate
Dichloro-s-triazine-2,4,6-trione,sodium salt
1,3-Dichloro-1,3,5-triazinetrione, sodium salt

plus other similar names. There may be a "dihydrate" after the name as that is the more common form (compared to anhydrous).

Dichlor is essentially Cyanuric Acid with two of the three hydrogen replaced with chlorine and the third hydrogen replaced with sodium (as seen in this link). In water, it produces the identical set of compounds as adding Cyanuric Acid and chlorinating liquid or bleach (except the chlorinating liquid or bleach add more salt).

Richard

[ths49286]

Thanks again I'll go look for some tomorrow.

[ths49286]

Before going out for the Dichlor this AM I went out and tested the pool water with the kit I have. Cl was a 7 ( it was 10 last night 2 hours after adding bleach), CYA was at 20. So i am thinking the CYA I previously added is slowly dissolving in the water. I have deceided not to add the Dichlor since I don't want the CYA to get to high. Just tested CL again 6 hours later and it is at 6. Will test CYA again tonight to see if it is increasing. I am apparently able to at least keep the CL from burning from sun , algea appears to be gone as pool is blue but still milky. I think I will add some clarifier to see if I can hasten the algae to get caught in the filter. The PSI has gone up 5 from last night. What about the clarifier?