2nd year, can't get rid of this stuff

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
Kitty_9098

2nd year, can't get rid of this stuff

Postby Kitty_9098 » Fri 22 Jun, 2007 14:00

Starting last summer we had something on the bottom of our pool. I would take water samples to be tested and everyone of them would say "balanced". I couldn't keep clorine in the pool though. From what I read on the internet it seemed that we had mustard algae. We tried Banish last year, didn't work. This year, we have tried Yellow Rid, Yellow Stuff and also kept the chlorine up between 5 and 10. Took a sample by this morning and the total and free chlorine were 6.5. Ph is 7.8 and the alkalinity was around 90 I think. We were gone for a week and nothing was put in the pool. When we got back, there was a little of this "stuff" and I thought maybe we were at the end of it. After my husband put in some tabs and shock, we got up the next morning to more of the "stuff". It seems to grow off the chlorine. The pool is a 20 x 40 above ground, and we've changed and cleaned everything except the hoses and the liner. Please help, can't seem to find anyone around here with answers.


Buggsw
Swimming Pool Superstar
Swimming Pool Superstar
Posts: 421
Joined: Sun 13 May, 2007 23:26

Postby Buggsw » Fri 22 Jun, 2007 14:47

I don't know what this "stuff" is. Perhaps it's pollen or dirt blowing into the pool.

Can't tell you much without a full set of readings.
Kitty_9098

2nd year, can't get rid of this stuff

Postby Kitty_9098 » Fri 22 Jun, 2007 15:47

water analysis done today: temp 80 saturation index 0.3 total chlorine 6.5 free chlorine 6.5 ph 7.8 total alkalinity 122 adj total alk 83 total hardness 246 CYA 131 Optimizer + 6 The system used to check the water is a Bio Guard water analysis system. However we are on chlorine. I was reading some other post and found the ones about not having enough sand in the filter. Someone said it should be 2/3 full but when they put in the 200 lbs recommended it wasn't atthe 2/3 mark. With thre recommended amount of sand in our filter it's only a little over 1/2 full. Could this be the problem and what problems are caused if you put too much sand in the filter? Thanks for your help!
chem geek
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Location: San Rafael, California

Postby chem geek » Fri 22 Jun, 2007 16:18

The problem is with having the CYA so high at 131. Just to keep algae from growing, you need an absolute minimum FC level of 10 ppm at your pool's CYA level. It would take a very high amount of chlorine to rid your pool of algae -- shocking to over 30 ppm FC. You have several options.

1) Shock your pool to 30 ppm FC and keep it there until the algae is gone and the chlorine level holds overnight. Then use an initial dose and then a weekly maintenance dose of PolyQuat 60 every week forever.

OR 2) Do a partial drain and refill of about 2/3rds of your pool water to dilute the CYA. You can then shock at a much lower level of chlorine. If you get your CYA down to 50 ppm, for example, then you can shock with 15 or 20 ppm FC and need to keep a minimum of 3.6 ppm though 5.7 ppm FC is a normal target at 50 ppm CYA. If you maintain your chlorine level, then you do not need to use an algaecide (unless you want to as insurance).

The reason your CYA level got so high was because you are adding it with your source of chlorine. Trichlor tabs/pucks have both CYA and chlorine in them, but whereas the chlorine gets used up, the CYA does not and builds up over time. If you don't backwash your filter, say because you don't have a sand filter and have a cartridge filter instead, then you don't dilute your water's CYA. For every 1 ppm FC you add with Trichlor, you add 0.6 ppm CYA as well.

To not build up CYA, you either have to regularly dilute your pool water or have to switch to a source of chlorine that does not have CYA. Bleach or chlorinating liquid will only introduce chlorine into your pool (lithium hypochlorite is another option, but is very expensive). Cal-Hypo is another option, but does increase Calcium Hardness. For every 1 ppm FC you add with Cal-Hypo, you add 0.7 ppm CH as well.

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