Cyanuric Acid Damages Plaster etc. ??

[JohnT]

A couple of articles from tricitypoolservice.com that might be worth reading:


CYA Issues

More CYA Issues

In brief, a couple of articles discussing the possibility that CYA may damage plaster. Prowl around, and you'll find that he's anti-SWCG too. I think the site is well worth the time to read.

 

[billybrobob]

Use straight bleach. Keep cya at recomended levels. OK.

 

[chem geek]

This study is controversial and has not been readily reproduced. I spoke to different sources about it including those at onBalance who tried to reproduce the study using large tanks with plaster coupons and found there to be no degradation of plaster surfaces at high CYA levels IF one properly accounts for CYA's effect on Total Alkalinity (TA). That is, if one adjusts the pH or other parameters such as Total Alkalinity (TA) or Calcium Hardness (CH) to make sure the saturation index isn't very negative, then one does not get degradation (it's actually more like the other way around -- if one does not try and lower the TA to more traditional levels near 80-120, then one does not see the degradation since adding CYA naturally increases the TA). In other words, the target range for TA should be higher when CYA is higher. For example, 100 ppm TA with 30 ppm CYA is equivalent to 160 ppm TA with 200 ppm CYA and is equivalent to 255 ppm TA with 500 ppm CYA (all at a pH of 7.5).

Also, no drop in CYA levels over time were seen, unlike the graphs in the study.

So we have a controversy here where Arch Chemical has these results but others do not (Chapman's results were also similarly controversial for the same reason). There was supposed to be a follow-up study done at the Cal Poly research center as mentioned here, but the CalPoly National Industry Research Center that first did research on spot etching in 2004 and was supposed to complete research on how different sanitizers (including those with CYA and biguanide) react with plaster in 2005 as described here or in 2006-2007 as described here but there is nothing I can find published on this latter study.

At this point, I believe we should be very skeptical of these results. They should be rather easily reproduced with plaster coupons and very high (500 ppm) CYA levels since one should register a significant and easy-to-measure drop in CYA levels over just 2 weeks. Anyone got some plaster coupons they can try? Of course, it will take a lot of dilution to measure the CYA level using our standard turbidimetric tube test.

Richard

 

[JohnT]

found there to be no degradation of plaster surfaces at high CYA levels IF one properly accounts for CYA's effect on Total Alkalinity (TA). That is, if one adjusts the pH or other parameters such as Total Alkalinity (TA) or Calcium Hardness (CH) to make sure the saturation index isn't very negative, then one does not get degradation. In other words, the target range for TA should be higher when CYA is higher. For example, 100 ppm TA with 30 ppm CYA is equivalent to 160 ppm TA with 200 ppm CYA and is equivalent to 255 ppm TA with 500 ppm CYA (all at a pH of 7.5).

I don't think that CYA/TA relationship is well known by pool owners or pool stores. I had my doubts about how accurate the stuff posted on the site is, but it seems to me that he is trying to actually understand pool chemistry instead of just blindly following conventional wisdom.

 

[Titanium]

JohnT,

Tri-City does seem to be above the normal caliber of pool service company in that he is aware of the CYA issue. But, then again, he seems to be pushing UV because chlorine is not effective (enough) against giardia and chrypto.

Titanium

 

[JohnT]

But, then again, he seems to be pushing UV because chlorine is not effective (enough) against giardia and chrypto.

I can't argue with him though. It's like anything else, risk vs. cost. Chlorine is not effective against those, and UV is probably the best option, but whether there is any risk, I don't really think so.

 

[chem geek]

I think UV makes a lot of sense in a public pool, but in a residential pool you aren't going to get Giardia or Crypto unless someone swims in your pool who is infected and has a diarrheal accident.

Tri-City also bashes SWG pools here and though it is important to point out the pros and cons of these systems, they do seem to be biased.