High Chlorine but still some yellow Algae on walls

[stevetuck]

Thanks to both Watermom and PoolDoc/Ben for the replies. Our pool is 12,000 gallons and six years old. We have owned the house for three years in August this year. We use stabilized chlorine tablets in an inline feeder. Standard Pentair Clean and Clear Plus cartridge filters plus the new Intelliflo variable speed pump. Our pH is usually around 7.2. We used to need to add acid to bring the pH down. Lately we have been having to add powder to bring the pH up. The mustard algae will start if the chlorine tests below 5. We can usually keep the algae away with chlorine around 8. You are correct in that we have been taught to believe that anything above 5 on the chlorine test is "high". We don't use strips. We use the Taylor Basic DPD test kit. From reading your forum we purchased the HTH 6 way test kit from Walmart so we could look at the CYA level. The test we did showed CYA at 150 or so. We then took a water sample to the pool store. They did use a strip and said the CYA was 110. We are wondering if we should abandon the stabilized chlorine approach and use bleach and Borax as you have written about? Then, as you recommend, let the CYA level drop on it's own over the next few seasons? Thanks for your help.

[PoolDoc]

To manage a pool with a CYA of 150, you'll *need* the K-2006; it's not optional (test kit page in sig). Read the "Best Guess" page, which explains. Without the K-2006 you won't be able to control your chlorine levels.

If would, please enter your pool data here:

Pool Chart Entry Form
Pool Chart Results

Operationally, high CYA can be a benefit IF you can control chlorine properly. With a CYA=150, you can add chlorine 1x per week, dosing to 15 - 20 ppm FC, and then letting it fall all week. That's about as easy as it gets!

[stevetuck]

I have entered the pool data and ordered the K-2006 test kit.

Thanks for your help.

[Watermom]

You're welcome!

[Watermom]

With a CYA of 110 or 150, you should definitely abandon the stabilized chlorine products. If you take a look at the Best Guess Chlorine Chart in one of our signatures above, you'll see the chlorine levels that you will need in your pool. You are also going to have to have the Taylor K-2006 or 2006C test kit as only that type of kit (FAS-DPD) can measure chlorine levels higher than 5. Your maintenance chlorine levels are going to be 8-15ppm and your shock level is going to be 25ppm. No wonder you have algae! You have not been keeping high enough chlorine levels for that high CYA. (You said above that you were able to keep the algae away whenever you kept your chlorine at least 8ppm. Now you know why!)

In your pool, each gallon of plain, unscented 6% bleach will add 5ppm of chlorine. Until you get a good kit, you can force your test kit to read higher by using a dilution method described here: Testing Without a Good Kit This is not meant to replace getting a good kit; it is just a temporary measure until you get the kit.

Test each evening and add enough bleach to get back to 25ppm. Continue to do this until you can go from sundown one evening to within two hours of sunrise the next day without losing more than 1 ppm. Run your pump 24/7 and clean the filter as needed.

You can order the kit through the test kit page in our signatures.