i've read somewhere on here that sodium hypochlorite (bleach) slowly oxidizes cya. i believe this is true. i lose 5-10 ppm of cya per month when i'm using only bleach to chlorinate.
CYA Disappearing
- Thread starter mlaspina
- Start date
It's true, but it's slower than that, more like 2-3 ppm per month at pool temps while in hot (104ºF) spas it's around 5 ppm per month. If you're seeing more than that, then it may be from water dilution. It's possible that something is accelerating the oxidation and we know it's somewhat faster at higher pH. As noted in the technical thread Degradation of Cyanuric Acid (CYA), every 1 ppm CYA loss would use around 2.5 ppm FC. So your 5-10 ppm CYA loss, if from oxidation by chlorine, would be 12.5 to 25 ppm FC per month or 0.4 to 0.8 ppm FC per day.
It's possible that the breakdown of chlorine in sunlight which produces hydroxyl radicals might accelerate the oxidation of CYA so maybe if your water is warm, is exposed to a lot of sunlight, and is higher in pH that you might see faster CYA loss. Are you sure you don't have rain overflow from summer rains or water dilution from backwashing?
It's possible that the breakdown of chlorine in sunlight which produces hydroxyl radicals might accelerate the oxidation of CYA so maybe if your water is warm, is exposed to a lot of sunlight, and is higher in pH that you might see faster CYA loss. Are you sure you don't have rain overflow from summer rains or water dilution from backwashing?
San Jose, CA. No substantial amount of rain (or snow, for that matter), so it isn't an overflow issue, and splashing water loss minimal last season.
Opened to 0 CYA after finishing last season at 50, confirmed with home test kit, friend's test kit, as well as pool store.
Pool was covered from October- April with an opaque safety cover, approximately 300 gallons added three times during that time to replace water that evaporated. Added 1 gallon of 12% chlorine each of those 3 times.
No substantial algae observed on opening to 50 degree water. pH 7.5, alkalinity 120.
Opened to 0 CYA after finishing last season at 50, confirmed with home test kit, friend's test kit, as well as pool store.
Pool was covered from October- April with an opaque safety cover, approximately 300 gallons added three times during that time to replace water that evaporated. Added 1 gallon of 12% chlorine each of those 3 times.
No substantial algae observed on opening to 50 degree water. pH 7.5, alkalinity 120.
That's a different situation since if you close and don't maintain the chlorine level then bacteria can grow and break down CYA. Sometimes this results in ammonia creating a huge chlorine demand, but other times it oxidizes the CYA all the water to carbon dioxide and nitrogen gas. Unfortunately, this isn't a controllable situation, otherwise it would be a way to reduce CYA.
Thank the pool gods I found this forum and that chem geek is a chem geek. After choking on 150+ cya for a couple of years with my cartridge filtered pool I woke up to zero cya this spring and sky high combined chlorine. This winter my filter housing blew up and it took a while to get the warranty replacement installed. By that time the pool, although skimmed and skummed several times, was suffering from the live oak leaf, flower and pollen drop we get in central Texas each spring. I had been doing some manual chlorinating but not enough. After the filter was fixed I fired it up and removed all the remaining visible junk but the water stayed cloudy and shocking it didn't do anything. The combined chlorine would shoot back up in a day after shocking. I did a Google of "high combined chlorine" and found chem geek's early posts about the issue and how it affected cya. I registered zero cya when I tested. I have been adding chlorine and watching the TC and CC levels change. They are now responding pretty normally. Just checked the ammonia content and it's now lower than tap water so I'll be throwing in some CYA and chlorine to see how things turn out. Previously all inquiries about lowering cya was to dilute it by draining out water because there was no chemical solution. Well there is, but it's not one you either want or can control. Thanks again, chem geek.
Well now, things are not acting as expected. As I said earlier I was going to throw in some CYA but prudently checked the level again since I had started up my regular 3" tablet chlorinator. Didn't want to overdo it. Imagine my surprise when I got 55-60ppm CYA. With a 15K gal pool and only 4 stabilized tablets dissolved since the test showed zero CYA it seems something is not following my foolproof plan. I waited a day and tested again with the same 55-60ppm result. Same kit all three times. The pool had been somewhat cloudy but that cleared up between the zero and 55-60ppm test results.
Any ideas on how this happened? What reaction would create CYA or perhaps what could render the test ineffective? I'm using a Taylor K-1005 kit. I'm taking a water sample to 2 pool stores to see how close we match up.
Any ideas on how this happened? What reaction would create CYA or perhaps what could render the test ineffective? I'm using a Taylor K-1005 kit. I'm taking a water sample to 2 pool stores to see how close we match up.
4 tabs in 15,000 gallons would be around 9 ppm CYA so yes, something is amiss. The test doesn't read well below 20 ppm and your test doesn't read below 30 ppm so when you said 0 it could have been just less than 30 ppm. Was the water in the tube crystal clear in seeing the black dot or did it have some cloudiness when filled up to the top?
The CYA test is sensitive to lighting conditions. The best approach is to have the sun to your back and hold the tube in front of you blocking the sun and look straight down. This is strong indirect light which is how the test was effectively calibrated.
So maybe you had 20 ppm so could still see the black dot at 30 ppm, then added 9 ppm to now have 29 ppm, and are looking under different lighting that has this 30 look more like 55-60. Still, that's further off than I'd expect even with such errors.
You should upgrade your test kit to the TFTestkits TF-100 or the Taylor K-2006, both available at the same tftestkits.net website. It has a better Taylor CYA test that measures down to 20 ppm.
The CYA test is sensitive to lighting conditions. The best approach is to have the sun to your back and hold the tube in front of you blocking the sun and look straight down. This is strong indirect light which is how the test was effectively calibrated.
So maybe you had 20 ppm so could still see the black dot at 30 ppm, then added 9 ppm to now have 29 ppm, and are looking under different lighting that has this 30 look more like 55-60. Still, that's further off than I'd expect even with such errors.
You should upgrade your test kit to the TFTestkits TF-100 or the Taylor K-2006, both available at the same tftestkits.net website. It has a better Taylor CYA test that measures down to 20 ppm.
Just adding that the cya test will test lower also if the water is cold and not given time to warm up.
chem geek said:
My initial 0 ppm test was as if the tube was empty - no turbidity visible at all. All tests' lighting conditions were done pretty much as you described. Since my background includes several years of manufacturing engineering working with chemicals and using visual criteria I'm aware of the hazards of haphazard test methods. With that in mind I wasn't sure what the temperature was for the first test (per Bama's comment) so I took a sample this morning and stuck it in the fridge to chill it well below 70F.
To push the test to total sloppy method I just squirted in the reagent, didn't mix it and started filling the sight tube.
I need a drum roll.................this poorly mixed and chilled sample measured 90 ppm. The test reagent is the same I've used for all 4 tests. :?:
I didn't get by the pool stores yesterday with a water sample but that will happen today. At this point I think I'll monitor things for several days and see when/if levels settle out.
Was the initial sample taken from at least a foot below surface level, I am not sure of the condition of your pool before the sample was taken, but if there was no circulation and the pool water was cold, and if there had been any significant recent water addition either rain or manually, that warmer fresh CYA free water could be floating on top of the CYA filled pool water.
Isaac-1 said:
I always sample after running the pool and Polaris for a hour or so and take them from an 18" depth away from any of the jets. No rain or water added lately.
FarmerJohn said:
Since we got the pool in 2005 I've always done my own testing and then gone to the pool stores as a checking measure. 90% of the time we are within 20% of each other which given the conditions at their stores (teenagers, messy testing station, lighting, etc.) and my own variability seemed reasonable.Today I got these results:
___________Taylor K-1005____Store #1____________Store #2
FC/ppm_________5______________1__________________10_______Laughing is permitted at this time
TC/ppm_________5______________1__________________10_______Laughing is permitted at this time
pH____________7.3_____________7.4_________________7.3
CH/ppm_________-_____________200__________________-_______My K-1005 CH test is really confounded by metal ions even using the tips from the testing section (Nature2 feature)
Total Hardness___-______________-__________________385______Store #2 said knowing the CH didn't matter
TA/ppm_________90____________100_________________95
CYA/ppm________90_____________60________________100
Copper__________-______________0__________________-________Copper ions come from the Nature2 and mess up CH testing but Store #1 said "0 ppm"
TDS____________-_____________1000_______________1000
I retested FC and TC when I got home and got 5 ppm.
BTW chem geek, I have a K-2006 and magnetic stirrer on order.
My pool is always 0 CYA at beginning of season and completely covered throughout the winter (no rain dilutes) . I do not add anything from October - March though ...maybe the previous posts explain that , something eats it .