CYA Levels

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That recommendation comes from the experience of many SWG users. For most, when the CYA levels drop below 70ppm, chlorine loss rates go up. I know this to be very true in my own pool and it's one of the early warning signs to me for when I need to test my CYA. As soon as my CYA level drops below 70ppm, I start to have to increase my % output to keep up my FC level. However, when my CYA level is at 90ppm (I tend to keep it on the high side), my FC loss rate is much lower and I can maintain my FC level with less % output.

@chem geek posted this many years ago. Read this post and follow the links to @mas985 's experiments he did in his spa. It very clear that the traditional chart of FC loss rate versus CYA concentration is not quite correct at the high end. It seems that there is an "anomalous" screening effect that is not accounted for in the basic chemistry of chlorine and CYA. Experience seems to show that higher CYA levels are much better for chlorine stability BUT you have to balance that against the risk of an algae bloom as higher CYA levels demand greater shock levels of chlorine to be effective. This has traditionally been the bane of most pool owners because service companies and pool stores will ignore CYA levels and then pools become much harder to control when algae gets going. But, because TFP teaches self-reliance and self-testing, many problems can be headed off early well before a pool ever goes pea soup green. SO in my own pool experience, I don't fear high CYA levels because I know that I'm going to catch problems before they ever start.
 
JoyfulNoise said:
That recommendation comes from the experience of many SWG users. For most, when the CYA levels drop below 70ppm, chlorine loss rates go up. I know this to be very true in my own pool and it's one of the early warning signs to me for when I need to test my CYA. As soon as my CYA level drops below 70ppm, I start to have to increase my % output to keep up my FC level. However, when my CYA level is at 90ppm (I tend to keep it on the high side), my FC loss rate is much lower and I can maintain my FC level with less % output.

@chem geek posted this many years ago. Read this post and follow the links to @mas985 's experiments he did in his spa. It very clear that the traditional chart of FC loss rate versus CYA concentration is not quite correct at the high end. It seems that there is an "anomalous" screening effect that is not accounted for in the basic chemistry of chlorine and CYA. Experience seems to show that higher CYA levels are much better for chlorine stability BUT you have to balance that against the risk of an algae bloom as higher CYA levels demand greater shock levels of chlorine to be effective. This has traditionally been the bane of most pool owners because service companies and pool stores will ignore CYA levels and then pools become much harder to control when algae gets going. But, because TFP teaches self-reliance and self-testing, many problems can be headed off early well before a pool ever goes pea soup green. SO in my own pool experience, I don't fear high CYA levels because I know that I'm going to catch problems before they ever start.
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thank you. just trying to understand why at the same CYA levels, UV would break down chlorine faster in a salt water pool vs a fresh water pool. Also, since the CYA ppm is high, is there any concern about swimming in the high chlorine levels?
 
The sources of the chlorine are all different. In the case of chlorinated cyanurates (dichlor and trichlor), chlorine is attached to the CYA already and is released into the water where is forms HOCl/OCl- . In Liquid chlorine (and calcium hypochlorite), chlorine is in the form of hypochlorite (OCl-). In an SWG, chlorine gas is produced and that has to dissolve into the water (fairly quickly) and then react to form HOCl/OCl-. SWG's add chlorine very slowly to the water and most returns are near the surface of the pool (most returns are 12" down). So there could be more loss associated with how the chlorine is added. It's an interesting feature but one that has never really been satisfactorily answered. Mark's studies indicated that there was no difference in the amount of chlorine produced by an SWG if the CYA was high or low.

As long as you are using the correct FC/CYA ratio, then it doesn't matter what the absolute FC or CYA levels are - the FC/CYA ratio determines how much HOCl (hypochlorous acid is the sanitizing form of chlorine in water) there is. The FC & CYA levels TFP recommends all create the same ratio - for an SWG pool, that ratio is 5%. For manually chlorinated pools, the ratio is 7.5%.
 
JoyfulNoise said:
The sources of the chlorine are all different. In the case of chlorinated cyanurates (dichlor and trichlor), chlorine is attached to the CYA already and is released into the water where is forms HOCl/OCl- . In Liquid chlorine (and calcium hypochlorite), chlorine is in the form of hypochlorite (OCl-). In an SWG, chlorine gas is produced and that has to dissolve into the water (fairly quickly) and then react to form HOCl/OCl-. SWG's add chlorine very slowly to the water and most returns are near the surface of the pool (most returns are 12" down). So there could be more loss associated with how the chlorine is added. It's an interesting feature but one that has never really been satisfactorily answered. Mark's studies indicated that there was no difference in the amount of chlorine produced by an SWG if the CYA was high or low.

As long as you are using the correct FC/CYA ratio, then it doesn't matter what the absolute FC or CYA levels are - the FC/CYA ratio determines how much HOCl (hypochlorous acid is the sanitizing form of chlorine in water) there is. The FC & CYA levels TFP recommends all create the same ratio - for an SWG pool, that ratio is 5%. For manually chlorinated pools, the ratio is 7.5%.
Click to expand...
thank you for the explanation. the haze in my head is starting to clear :)
 
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