Zero FC Pool is crystal clear

[Hurricane1938]

Hi,
As you know this is my first post. I've been a pool owner for 18 years and never had a problem like this.

Background: This past winter was uncommonly warm. With the porous Loop-Loc cover, I'm accustomed to a green pool when opening it, but this year it looked like pea soup and smelled like a sewer. Initial CYA reading was 0.

After a lot of work I've gotten it clear and added ~24oz of Polyquat 60%.

Now, the pool specs:
27,000 gallon, 18X36 inground vinyl pool, DE filter, Hayward off-line chlorinator, heated with natural gas.

Pool water is ~80F and clear. Taylor K-2600 readings:
FC=0; CC=0.8; pH=7.4; Alkalinity=110; Hardness=170; CYA=75

Circulator is running 24hrs. Chlorinator is set to Full with 3" tabs.

I have been adding ~2.8 gal of 6% plain bleach each evening, but by morning my FC=0.

Even with the Polyquat, if I'm away for a few days, I will sometimes see a small amount of green algae, until I dump several gallons of bleach and brush the pool.

I’m grateful that the pool is clear and swimmable, but what should I do now.
Thank you!

Peter

[aylad]

Hello, and welcome to the forum!

If you use a chlorinator, then odds are really good that your CYA was high at closing, and the algae outbreak that happened over the winter biodegraded the CYA. When that happens, one of the possible by-products is ammonia, which will create a HUGE chlorine demand. We've seen lots of cases of this, but never more than we have this year, and I think it's mostly due to the unseasonably warm winter.

At any rate, what you need to do, whether it's ammonia or not, is to shock the pool by bringing your chlorine level up to 20 ppm and holding it there as consistently as possible until the algae that you see is gone, and until you can go from sundown one evening to sunup the next morning without losing more than 1 ppm of chlorine. If you have ammonia in the pool, this may take awhile, but that chlorine demand needs to be overcome before closing, otherwise you'll have a real mess on your hands next year. Test as often as possible, and add more chlorine to get back up over that 20 ppm mark, because the more consistely you hold it at shock level, the faster the demand will be overcome. 2.8 gallons of bleach in 27K gallons is only raising your chlorine by just over 6 ppm, so that's not nearly high enough to kill off anything growing in the water. In fact, with a CYA of 75, your minimum chlorine level should be 5 ppm.

I would use bleach for the shocking--if you turn the chlorinator up, you probably still won't be able to achieve 20 ppm all at one time, and you're just raising your CYA higher--which in turn will require you to maintain your chlorine higher.

[PoolDoc]

I have been adding ~2.8 gal of 6% plain bleach each evening, but by morning my FC=0.

Increase the dose to 8 gallons -- about 20 ppm -- and brush after you dose. Discontinue use of the polyquat will doing this; that much chlorine will break the polyquat down.

Test chlorine levels the following evening, and add 1 gallon of bleach for each 2 ppm below 20 ppm; ie. if FC=10, add 5 gallons. Continuing dosing in this manner for 5 days. Brush the pool completely again at some point after the first large dose.

Then, skip one dose, and test FC both evening and the following morning. You're checking to see what the overnight (no sun) chlorine loss is.

Let us know.

Also, you may want to read this page:
http://www.poolforum.com/pf2/showthread.php?18597 (Adding-Borax-to-Make-your-Pool-Resistant-to-Algae)

[Hurricane1938]

Thank you Janet and Ben.

In general, I've always been very good with chemistry. I had a world class chemistry set in high school and college; took general chemistry, biochemistry and physical chemistry, but that was a long time ago! This experience underscored the incredible value of this forum and your help. My problem, like anumber of other participants in the forum and this treatment strategy is worlds beyond the knowledge and skill of the pool store people in my area of Long Island, NY.

Peter

[PoolDoc]

You're welcome!

[aylad]

Just want to add my thanks to your for your subscription to help this forum keep going!!

[Hurricane1938]

Your welcome!!
Peter

[Hurricane1938]

Taylor K-2006 readings this morning: FC 15, CC 0.3, pH 7.6, TA 130, CH 170, CYA 65. Temp 78F, water is clear, no visible algae.

Two nights ago I added ~9 gal. of 6% bleach. Next morning FC=9; by evening FC=2. Last night, again, I added ~9 gal. of 6% bleach. This morning FC=15; by evening FC=7.5. I will again add ~9 gal. of bleach.

I feel like I'm making progress, but I'm not quite there yet.

Thanks again for your interest and help!

Peter

[Watermom]

The FC and CC comparisons that you need to note are the numbers taken an hour after the evening dose of bleach and the readings taken the next morning within two hours of sunrise. Seeing what kind of overnight loss you have is an essential piece of information.

[Hurricane1938]

The FC and CC comparisons that you need to note are the numbers taken an hour after the evening dose of bleach and the readings taken the next morning within two hours of sunrise. Seeing what kind of overnight loss you have is an essential piece of information.

Several nights ago I added ~9 gal. of 6% bleach. Embarassingly, with the high levels of FC, I ran out of the reagent to check FC! I haven't added any bleach since then.

Last night readings: Temp 78F; FC 7.4; CC 0.4; pH 7.5; TA 130; CH 170; CYA 75

This morning FC 7.2

Am I right to be encouraged by the steady (within measurement accuracy) FC level?

CYA level seems to have declined slightly (9 days ago it was ~75-80). My Chlorinator is turned off. Will CYA gradually come down if my FC is coming from bleach and not stabilized tabs?

Thanks again for your help, it really is appreciated!

Peter