too much cyanuric acid

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??

too much cyanuric acid

Postby David522005 » Sat 15 Nov, 2008 20:18

I have been told by one dealer that my very high cyanuric acid reading (200, recommended range 30-70) is a health hazard, and that I will have to dump half of the water and 'start again'. Another dealer tells me that it isn't a problem. What are the implications of having a high level? (salt water pool).

chem geek
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too much cyanuric acid

Postby chem geek » Sun 16 Nov, 2008 04:11

Higher levels of Cyanuric Acid (CYA) do lower the active chlorine (hypochlorous acid) concentration unless the Free Chlorine (FC) level is proportionately raised, but most bacteria are very easy to kill so it's not exactly a health hazard as far as uncontrolled bacteria growth is concerned (though it does slow down kill rates so person-to-person transmission risk may be increased). It does, however, make it more likely for your pool to develop algae unless you use a supplemental algaecide (with weekly maintenance dose) such as PolyQuat 60 or use a phosphate remover. With an SWG, you might just find that there is excessive chlorine demand (from nascent algae growth). You could also be lucky and have your water be low in algae nutrients (phosphates and/or nitrates).

It is true that the way to lower the CYA level is through dilution of the water. For SWG pools exposed to full sun, a CYA level of 60-80 ppm, usually 70-80 ppm, is more appropriate, but you need to maintain an FC level that is at least 5% of the CYA level, so around 4 ppm FC for those CYA levels. That will prevent algae growth without the need for supplemental algaecides.

You can learn more about the chlorine/CYA relationship and maintaining a pool at the Pool School. Technical graphs of the active chlorine amount as a function of pH in pools without CYA (the traditional industry graph) and pools with CYA (that isn't currently being taught) are shown here. The derivation of why the FC/CYA ratio is proportional to the active chlorine concentration and a description of the chlorine/CYA relationship is here.


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