algea in pool

[tara15]

Hello,

I have a 15,000 gallon above ground pool. I have had many algea problems this year. i have used the polyquat, shocked it and no luck. it was blue for one day, and then green again. here are my test results as of 10 minutes ago

ph. 6.8
fc 7
ta 80
cya 100

ive tried shocking all the time, we have the chlorinating tablets in the pool. i just dont know what to do anymore. any help will be appreciated.

thanks

[ivyleager]

With a CYA of 100, you're going to need to shock (super-chlorinate) up to the 20-25ppm level and hold it there until you no longer have any combined chlorine (CC). I have a feeling you've been yo-yo'ing w/ your shocking. One gallon of 6% bleach will raise the chlorine 6ppm per 10,000 gallons. So, on a 15K gallon pool, one gallon should raise you 4.5ppm. You'll need about 5 gallons of bleach in your pool to initally raise it up to 20-25ppm level. Make sure you're running the filter 24/7 during this process. Backwash as needed as algae can gunk up the filter.

Also, your pH is too low and may be lower than 6.8. Most test kits don't test below this level, so I'd do this first. You'll need to bring that up to 7.2 at least.

Stop using the chlorinating pucks. They drive up CYA and drive down pH. Begin using bleach only for chlorinating. You'll find a lot of information in the chlorinating section http://www.poolforum.com/pf2/forumdisplay.php?f=132
as well as tons of tips to get you started http://www.poolsolutions.com/tips/10things.html


Good luck.

CaryB

[tara15]

ok. so i first added about 4 pound of baking soda to the pool and retested about a half hour later. the readings are as follows

fc 10
ta 120
ph 7.2
cya 100(still)

i added about 2 gallons of bleach for now since that is all i have on hand until i go to the store. do you still think i need 5 gallons? also, we noticed when we didnt have the pucks in the floaters, the algea problem got worse and we were shocking more. how often should i add bleach to the pool? when is it safe to go back in the pool?

[Watermom]

You say "still 100" when referring to your cya reading. It isn't going to come down - unless you do a partial drain. If you use more pucks, it is going to continue to rise which you don't want. Take a look at the Best Guess chart in the following link.

http://www.poolforum.com/pf2/showthread.php?t=365

Yes, you need to shock up to 25 since your cya is so high or you won't get rid of the algae. How often? Test at least 3x a day (more won't hurt!) and EACH TIME add enough bleach to get your cl level back up to 25. The key to killing algae is to sustain the high reading and not let it yo-yo up and down. In a pool this size, each quart of 6% bleach will raise the cl by 1 ppm. Also, run your pump 24/7 for now. After your algae problem is gone, you'll need to keep your cl between 8-15 all the time because of your high cya or you'll have another algae bloom.

Another option is to do a partial drain and reduce your cya to about 50 which would be ideal. It is up to you. Partial drain or just run higher than normal cl readings. Either way will work - it is up to you.

Your ph and alk are OK now. If your ph drops any, you'll want to use Borax to raise it instead of baking soda.

[tara15]

the only reason i said still 100 for cya was that the test strips said that the ph and alkalinity affected the cya reading. also, where can i get test strips that give you a number higher that 10 for free chlorine? do i have to buy them at the pool store? i also have a dog who like to swim in the pool. is it safe for her to swim if she doesnt mind slightly green water or should i wait?

thanks

[Watermom]

We don't recommend teststrips because they aren't very accurate. Most of us use the kit that Ben sells at the sister site to this forum www.poolsolutions.com. It WILL test high cl levels which you're going to need to be able to do if you decide to keep your cya of 100. At the very least, buy the 5-way drops based kit at Walmart for about $15. It won't test cl higher than 5, but you can dilute the sample and make it test higher. However, just be aware that with each dilution, you do lose some accuracy. To dilute - take one part pool water and two parts distilled water, mix them together and then test as usual. Then multiply the result by 3. (If it were my pool, I'd do the partial drain and lower cya to 50. Just my opinion.)

About the dog - dogs swim in green ponds all the time so............. but, I probably wouldn't let it swim in the pool when it had been shocked so high.

Hope this helps. Keep us posted how things are going.