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?

[chem geek]

I suspect your CYA will stay around 20 as you technically added 17 and presumably started from 0, but it's safe to wait and you are right that it does provide a lot of protection even at 20.

As for the clarifier, it will speed things along by clumping dissolved algae remnants but technically it is unnecessary if you wanted to just use chlorine and be patient since the chlorine will continue to break down the algae. It's up to you. Just don't add too much -- follow the directions on the bottle and you can then vacuum to waste if there's sediment that settles. It usually takes 3-4 days to clear up an algae bloom and sometimes up to a week depending on the size of the bloom.

You might consider cleaning (backwashing) your filter as you've noticed a big rise in pressure.

Richard

[ths49286]

I will backwash again today and have vacumed the bottom a couple times as I know there is stuff on the bottom even tho I can't see it. I think now that the chlorine is'nt burning off within a couple days it should be clear. I opened it sunday afternoon and today is the first day that I have been able to keep chlorine in it 24 hrs. that should make a big difference. I was in a hardware store today and saw 10% chorine for 2.25 a bottle, I am going to go and get some. This afternoon the pool is really blue( yet milky), how high should I take the chlorine level up for tonight and tomorrow? It was 85 and sunny today and is supposed to be the same tomorrow. Thanks richard

[chem geek]

Maintaining 10 ppm FC at 20 ppm CYA should be fine for clearing the algae though Ben's chart says 12 ppm FC in the "shock" column, but you need to maintain that level so go a bit higher as needed (say, to 15 ppm FC in the morning, but not higher than that) and check it during the day (if possible). It sounds like the chlorine usage is declining so that is good.

I assume you are running the filter 24/7. Using a skimmer sock might help as well (will reduce how much backwashing you need to do). You are already vacuuming to waste so that's also good. There's just a lot to remove from your pool -- one way or the other.

Richard

[ths49286]

I am running the filter 24/7, I do have some skimmer socks but have not used them yet. Obviously the theory is that the minute stuff that gets thru the socks is then trapped by the filter,those are some tiny particles. I am going out for my evening reading now, unfortunately I have to work tomorrow so will test early and add CL to get it up to 12-15 during the day. I also saw somewhere that CYA is quite acidic so that must be why my PH has dropped to 7 from 7.4. I will also bump that up and post my numbers if anything seems outa whack. Thanks again.