purple algae again

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

purple algae again

Postby pool girl » Sat 03 Jan, 2009 09:51

Me again, actually it test high for "Cyanuric acid" What is this and how do we lower it. As we are told to drain the pool.

chem geek
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purple algae again

Postby chem geek » Sat 03 Jan, 2009 15:48

Unfortunately, you can only readily lower Cyanuric Acid (CYA) by dilution, so a partial drain/refill. You can learn more about how to maintain your pool by reading up at the Pool School. To prevent algae in the future, you need to either maintain a sufficiently high Free Chlorine (FC) relative to the Cyanuric Acid (CYA) level -- for a manually dosed pool that means an FC that is at least 7.5% of the CYA level at all times. Either that or if you want to use a lower FC level or not care about the CYA for as long then you need to use a supplemental algaecide (e.g. PolyQuat 60) or a phosphate remover at extra cost. Or you can regularly dilute the water through more frequent or longer backwashing (if appropriate for your filter) or intentional dilution (regular partial drain/refill) to keep the CYA level from building up.

Chemical facts that give you an idea of how your CYA level could have built up quickly are the following:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.


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