Thanks for the info on that. While I have not tried turning off the SWCG and just doing chlorine I did replace the SWCG itself and CYA dropped to zero with the new cell. I got a new cell because I thought the old one was defective. It seemed like it was not keeping up with chlorine as I always had to add more.This is a really unusual situation. Normally CYA is a fairly stable molecule and it doesn't degrade fast by photolytic degradation pathways and it doesn't normally undergo electrolytic degradation in the conditions in an SWG cell.
Did you try swapping to another chlorine source and turning off the SWCG cell? If so did the CYA level stabilise? The reason that I ask is that CYA can undergo electrolytic degradation but typically it happens under very specific conditions, the papers I've read were using a special boron doped diamond electrode for example. There are a few papers on this that are in relation to water treatment techniques to destroy triazine ring based pesticides and CYA shares that core structure of a triazine ring while being safe to handle. So it was used in the method development. The method used was able to destroy 50ppm of CYA by electrochemical degradation in 12 hours on a lab scale and they found that the most efficient supporting electrolyte to do this was 0.05M sodium chloride, aka a 3000ppm salt solution. It's really unlikely, but it's not impossible that your chlorinator is faulty and if so it may be be degrading the CYA and this may be exacerbated as you are running it for long periods.
It has been driving me crazy I have never seen the CYA disappear like this before, my pervious pool I never had an issue. I really wanted to go to a circupool SWCG as I put one in on my other pool and it was awesome but they have quadrupled in price and I just could justify that on a new pool.CYA is a very stable molecule. It's one of the degradation products for some pesticides and it is considered a persistent pollutant in environmental applications. So something unusual appears to be happening. The actual SWG cell is basically just the electodes. If there is something really out of whack with the system, I think it's more likely to be in the power supply. I do still think this is incredibly unlikely, but perhaps worth a try just to see if it still happens. The CYA disappearing is inconvenient but for it to happen, repeatedly with different brands and in the absence of dilution in a short period of time, means that something is breaking it down. That could be biological, but as Mknauss pointed out, your free chlorine levels preclude that. It could be a seriously defective SWCG although it's very unlikely. I think it's unlikely that there is a chemical agent powerful enough to break down CYA in the pool as I think you would be seeing all sorts of issues with your testing reagents if nothing else and probably issues with skin irritation degradation of pool equipment and so on. The only other option really is that something in the pool water is acting as a catalyst to allow it to break down fast by either photolytic degradation or in a normally functioning SWCG. That is something that would be almost impossible for a home pool user to work out, but there are scientists beavering away working on systems to break these chemicals down and they probably would be interested in identifying a naturally occurring catalyst for the process as it would greatly reduce costs. All scientific papers nominate a corresponding author, so it shouldn't be too hard to put you in touch with someone with a research interest in this area if you eliminate all the other likely options.
Thanks that is grate info I appreciate the advanced answers to this unique problem. I keep all my testing kits in the house so they are stored in a cool dry place. I also use the TFT kits and I believe they use taylor reagents. I agree that's not the issue. You are correct when I lost cya nothing else dropped so I was able to rule out loss by water overflow.View attachment 380039So generally speaking the additions you are making are matching the test kit results but the CYA level is not stable. That tends to suggest that the product is OK and that the reagents you're using are ok. I have seen some issues with dud reagents from one of our local australian test kit manufacturers when they first started out. I think they now repack the Taylors reagents. The CYA reagent is Melamine dissolved in water. Melamine is also a triazine ring based molecule but it has three amine groups pendant off the rings carbon atoms. Melamine degrades to CYA and ammonia, so if the reagents go off, they don't form a cloudy complex and the test doesn't work. I don't know if the Taylors reagents are stabilised to prevent the melamine from degrading but they seem to hold up pretty well. As a general rule it's worth storing the kit in a cool place and keep the reagents in the box where it's nice and dark.
I don't think that the reagent breaking down is your problem here though as the results are fairly consistent with the additions. The test is quite subjective, I would say that if you lined up several people with the same samples you could easily get +/- 10ppm variability in the results and you seem to be getting better accuracy than most. So your test results are a reasonable match with your additions. You appear to be consuming CYA at about 10-15 ppm per week. To get that sort of drop from dilution you would need to be swapping out nearly 5000 gallons of water. I suspect you would notice and as you say it would show very clearly in all your other test results.
How often do you clean your cell ? What do you clean it with ? Most cells these days use titanium plates with a rare earth coating. If you strip off the coating the electrolysis is less efficient and the output will drop but you will also be left with titanium plates. Titanium is funny stuff, it doesn't corrode much because it tends to form a very stable passivated oxide layer on the surface. Titanium dioxide has been used as a catalyst in degrading triazine based pollutants. I really am starting to think that it would be worth running on liquid chlorine for a few weeks to see if the CYA levels stabilise.
Florida heat, sunlight, and rain are a different animal for CYA than other parts of the country. I have learned to test it frequently in the summer, and have it on hand so I am ready to address its loss. I don't know why it goes. Could be the water temp, the uv, the rain... But it does go. Test more often, add as needed.Thanks that is grate info I appreciate the advanced answers to this unique problem. I keep all my testing kits in the house so they are stored in a cool dry place. I also use the TFT kits and I believe they use taylor reagents. I agree that's not the issue. You are correct when I lost cya nothing else dropped so I was able to rule out loss by water overflow.
The pool was brand new in Jan, I cleaned my old cell twice and installed a new cell Sep first and the issue still occurred. I cleaned by placing in a bucket with acid and water for 10min. I'm starting to think that there is really something wrong with the power unit now as even when I check directly from the returns I am only getting a CL of 1ppm with the new cell. At that rate at 50gpm for 24hrs that would only give me an output of 3.6ppm when it should be putting out 5.8.
I need to refill my chlorine and I will turn off the SWCG. I'm going to retest this weekend so hopefully I can do both to monitor the results. Appreciate the help.
That is exactly what I do, I keep 7.5gal of liquid chlorine at all times.Florida heat, sunlight, and rain are a different animal for CYA than other parts of the country. I have learned to test it frequently in the summer, and have it on hand so I am ready to address its loss. I don't know why it goes. Could be the water temp, the uv, the rain... But it does go. Test more often, add as needed.
Also, if the SWG "falls behind," it won't catch up. When that happens I add LC to get it just above the high end of the target. Then I test frequently and adjust SWG runtime and percentage as necessary to maintain LC levels.
I suspect it's either a faulty unit or there may be some sort of catalytic effect from something in the pool water. What that would be I have no idea, I think the power unit is more likely.Did my checks again this weekend and CYA hit 70 so everything is still good. I will continue to monitor CYA but it appears for now that the SWCG is indeed causing the extreme drops in CYA I have been experiencing here but I think it still requires longer evaluation to confirm. I have reached out to Jandy for support as I believe the power unit is faulty and is what it making my cell eat the CYA.