chem geek wrote:firehall90 wrote:The idea of draining a pool to lower cyanuric acid is a bit outdated. A 40k pool can have this level reduced by 100ppm by adding 2lbs of lye. It will in effect raise the pH, but only slightly and lye can be purchased at most home improvement stores in the plumbing department as a drain unclogger. Only pure lye should be used as any other product will contain additional metals such as alluminum. the ingredient will list 100% calcium chloride if it is ture lye. The same is used in water treatment at plants the utilize isocyanuric acid to stabilize chlorine.
What? It is true that a high pH of 9-10 AND high levels of chlorine can oxidize Cyanuric Acid and is sometimes done for water treatment, but this isn't something to be done safely in a pool. The high pH can create calcium carbonate scale and the very high chlorine levels required can oxidize and corrode what is in the pool (including metal).
Lye is just sodium hydroxide (not calcium chloride -- you are thinking of calcium hardness increaser) and raises pH. There is NOTHING special about lye. Any strong base can be used to raise the pH, even 20 Mule Team Borax (sodium tetraborate decahydrate). Adding 2 pounds of lye to a 40,000 gallon pool that has a TA level of 150 ppm with CYA of 100 ppm would raise the pH from 7.5 to 8.9. If the pool was near saturation with calcium carbonate to protect plaster surfaces, the index would get to about +1.5 which would very likely cause scaling.
Also, the CYA will not drop just from high pH alone. It requires either an enzyme-driven pathway or a lot of oxidizer in the water. This scientific paper talks about the biodegradation of CYA by bacteria and this link describes that pathway in more detail, but this isn't a very reliable way to degrade CYA in a pool and it produces a LOT of ammonia that then needs to be oxidized or otherwise removed. [&u=%2Fneurl=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1tahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,075,094.PN.&OS=PN/4,075,094&RS=PN/4,075,094]This patent[/url] describes the oxidation of CYA by chlorine at a pH of 9-10, but it takes a LOT of chlorine to do so -- needing a minimum of 2.5 times as much FC as the CYA you want to eliminate (so 250 ppm FC to get rid of 100 ppm CYA) -- clearly impractical.
Apologies for the calcium chloride, and for references I provide these:
Patent US 5,194,162 http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,194,162.PN.&OS=PN/5,194,162&RS=PN/5,194,162
Patent US 4,389,318 http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN%2F4389318
Patent US 5,021,186 http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN%2F5021186
The later two referred to by the first as supporting references. The pH of 5.0 to 7.5 is markedly different than 9.0-10. The addition of sodium hypochlorite only assists in speeding the process. The idea here is simply to reduce the CYA, not increase the pH…it is simply a side effect of reducing the CYA concentration which increases the pH. Once the CYA is reduced he can adjust the pH as needed.