I thought I would give those who are interested an update on some testing that I have been doing regarding CYA levels and chlorine.
First a summary of the testing that I did in this thread.
- Running my spa with the SWG at CYA levels from 45-80 ppm showed no change in chlorine production.
- Extinction rates seemed to improve better than what theory predicted for higher CYA levels.
- Unfortunately, I could not get consistent results from some of the extinction tests that I did.
So after the testing I did early in the summer, I lost exclusive use of the pool and spa since the kids were off from school .
About 3 weeks ago, I decided to raise the CYA level in the pool since at least some of the testing showed an improvement with higher CYA levels. At the time I thought my CYA level was around 45 ppm since that was what the last test showed me. I added 5 lbs of CYA which should have brought the level up to about 75 ppm but when I tested it again after 2 weeks, it showed only 50 ppm. Even after 3 weeks, it was still 50 ppm so I added another 5 lbs which brought the CYA up to 80 ppm. During the summer, I lost about 25 ppm of CYA somewhere. Still a mystery.
Anyway, after I raised the CYA in the pool to 80 ppm, I noticed that the chlorine level changed from 2.5 ppm to over 6 ppm. I have since dropped the SWG setting from 60% to 35% and the Chlorine level still increased to 8 ppm. Some of the increase was due to using the solar cover more often so I really couldnâ€™t conclude anything from that change.
So I thought about an easy test I could run that would show how well different levels of CYA would protect chlorine without extraneous factors getting involved with the test. Since I am now at 80 ppm of CYA, I thought about dilution. Dilution would accomplish several things. It would reduce the CYA and chlorine levels by the dilution ratio while still keeping the chlorine to CYA ratio constant. According the Chemgeek formulas, this should keep a fairly constant level of HOCL independent of dilution ratio. It would also expose the samples to same sun exposure on the same day. So I used three 5 gallon buckets side by side with tap water for dilution, yes distilled water would have been better but I thought I would try this first:
First bucket: No Dilution CYA = 80 ppm, CL = 8 ppm
Second Bucket: 1:2 Dilution, CYA = 60 ppm, CL = 6 ppm
Third Bucket: 1:1 Dilution, CYA = 40 ppm, CL = 4 ppm
I let them sit in the sun for a full day and then tested the chlorine again.
First bucket: No Dilution CYA = 80 ppm, CL = 6.5 ppm a 1.5 ppm loss (19% extinction)
Second Bucket: 1:2 Dilution, CYA = 60 ppm, CL = 3.5 ppm a 2.5 ppm loss (42% extinction)
Third Bucket: 1:1 Dilution, CYA = 40 ppm, CL = 0.8 ppm a 3.2 ppm loss (80% extinction)
So even though the first bucket had the highest chlorine level, it still lost the smallest amount of absolute chlorine. If true, this is clearly a significant economic benefit to running higher CYA levels.
This means that you could run an 80 ppm CYA pool with half the chlorine cost as a 40 ppm CYA pool even though the residual is twice as high. However, the buckets are only 12" deep so the results for a 5' pool may be different.
I think the biggest revelation, unless I am missing something, is that this should be true for bleach run pools as well which kind of goes against current thinking.
I for one am pretty convinced that running at higher CYA is better but I am curious about levels exceeding 80 ppm. At some point there will be diminishing returns and possibly adverse effects. It may be possible to curve fit the data, one of the reasons I chose three buckets, to see if there is some point where the increased gain is so small it just doesn't matter that much.
If I have time, I may try it again with smaller containers and use distilled water instead of tap water.
Can anyone identify any flaws in the test or conclusions?
Also, would anyone else be willing to do the same test to verify the results.