Newbie with a Green Pool
- Thread starter FresnoPoolDad
- Start date
I am doing some research just trying to understand the chemistry behind the Chlorine / CYA chart and came across an interesting article. http://www.ppoa.org/pdfs/PrP_Cyanurics - Benefactor or Bomb.pdf.
The author argues that CYA should be kept to no more than 20 ppm in a pool maintained by hand. I'm skeptical based on what I am reading here but would love to hear your take on his claims.
Claim 1 -- that most of the "staying" power of CYA is achieved at 20 ppm.
I've attached his chart (the bottom graphic) which purports to show (1) that even at 70 ppm CYA FC will decrease by 9.9% per hour; (2) that the stabilizing power of CYA increases exponentially at first and then flattens out so that at about 30 ppm FC loss is 10% per hour (i.e. only a tiny bit worse than at 70 ppm). He does not specify temp / sunlight for the chart. Is this consistent (or at least in the ball park) with your observations of your own pools? If he is right and I am understanding all of the numbers, a pool at FC 5 ppm and 50 CYA would lose .5 ppm in the first hour resulting in FC 4.5 , after 2 hrs = FC 4.1, 3 hrs = FC 3.6, ... 8 hrs = FC 2.2. If this is true, the a starting at 10 ppm FC and 50 ppm CYA would hit negligible FC in less than 48 hours? Although maybe the chart only refers to sunlight hours in which case you'd get 3 -4 summer days before you had nearly zero FC. Sound about right?
Claim 2 -- that CYA dramatically reduces the oxidizing (and to a much lesser extent the sanitizing) power of FC.
His second chart (the top graphic) purports to show that a pool at FC 4 @ CYA 40 has the oxidation effectiveness equivalent to FC .4 @ 0 CYA (ph 7.4 / temp 76F). He also claims that at 70 ppm CYA and above any FC number no matter how high gives an effectiveness equivalent to FC .2 @ 0 CYA. The assertion jibes with what everyone has been saying about CYA - that at a certain level it becomes *practically* impossible to get any ozidizing power out of Chlorine no matter how much you put in. However, he seems to be claiming something more -- that it is *actually* impossible to get more than a FC .2 equivalent no matter how high you raise the FC. Does this square with your experience.
He cites a bunch of studies which may or may not be valid. I am really more interested in first hand experience. Once I get my test kit I am going to do a little experiment ...
The author argues that CYA should be kept to no more than 20 ppm in a pool maintained by hand. I'm skeptical based on what I am reading here but would love to hear your take on his claims.
Claim 1 -- that most of the "staying" power of CYA is achieved at 20 ppm.
I've attached his chart (the bottom graphic) which purports to show (1) that even at 70 ppm CYA FC will decrease by 9.9% per hour; (2) that the stabilizing power of CYA increases exponentially at first and then flattens out so that at about 30 ppm FC loss is 10% per hour (i.e. only a tiny bit worse than at 70 ppm). He does not specify temp / sunlight for the chart. Is this consistent (or at least in the ball park) with your observations of your own pools? If he is right and I am understanding all of the numbers, a pool at FC 5 ppm and 50 CYA would lose .5 ppm in the first hour resulting in FC 4.5 , after 2 hrs = FC 4.1, 3 hrs = FC 3.6, ... 8 hrs = FC 2.2. If this is true, the a starting at 10 ppm FC and 50 ppm CYA would hit negligible FC in less than 48 hours? Although maybe the chart only refers to sunlight hours in which case you'd get 3 -4 summer days before you had nearly zero FC. Sound about right?
Claim 2 -- that CYA dramatically reduces the oxidizing (and to a much lesser extent the sanitizing) power of FC.
His second chart (the top graphic) purports to show that a pool at FC 4 @ CYA 40 has the oxidation effectiveness equivalent to FC .4 @ 0 CYA (ph 7.4 / temp 76F). He also claims that at 70 ppm CYA and above any FC number no matter how high gives an effectiveness equivalent to FC .2 @ 0 CYA. The assertion jibes with what everyone has been saying about CYA - that at a certain level it becomes *practically* impossible to get any ozidizing power out of Chlorine no matter how much you put in. However, he seems to be claiming something more -- that it is *actually* impossible to get more than a FC .2 equivalent no matter how high you raise the FC. Does this square with your experience.
He cites a bunch of studies which may or may not be valid. I am really more interested in first hand experience. Once I get my test kit I am going to do a little experiment ...
Attachments
- Jun 14, 2012
- 2,668
- Pool Size
- 13500
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool Edge-40
Its funny but reading a bit more on TFP I found this thread raising the identical questions with the identical graphs! 
Here http://www.troublefreepool.com/more-about-recommended-cya-levels-t48502.html and Here http://www.troublefreepool.com/interesting-cya-article-t21910.html and here http://www.troublefreepool.com/pool-water-chemistry-t628.html Search and ye shall receive. Not that I understand much of anything that chemgeek writes in the last link. But at least I know what I don't know and that is always a good place to start.
Here http://www.troublefreepool.com/more-about-recommended-cya-levels-t48502.html and Here http://www.troublefreepool.com/interesting-cya-article-t21910.html and here http://www.troublefreepool.com/pool-water-chemistry-t628.html Search and ye shall receive. Not that I understand much of anything that chemgeek writes in the last link. But at least I know what I don't know and that is always a good place to start.
FresnoPoolDad said:
I'm going to say this author is comparing the FC/CYA relationship for a board spectrum of pools mainly high bather pools. What he is saying is that the FC/CYA relationship needs to be adjusted for each pool and I don't think anyone here would argue against that idea. The FC/CYA chart that is used here at TFP is a great guide for most residential pool owners. It is up to each pool owner to figure out what is the best FC/CYA relationship for their pool. Pools in a sunny hot climate will need more CYA to protect the chlorine from the sun as compared to a pool in a cool shady environment. In your case we would suggest to bring the CYA up to 50 as a starting point and let you learn how your pool uses its chlorine. You would most likely have to add chlorine every one or two days but it would stay more consistent this way.
I believe most people that have their pools dialed in lose about 2-3 ppm of chlorine a day. They add enough chlorine usually in the evening to accommodate this loss. When the chlorine level is raised higher you will lose more chlorine from the sun. So if you wanted to dose every other day you would use a little more chlorine than dosing everyday.
- Jun 14, 2012
- 2,668
- Pool Size
- 13500
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool Edge-40
76 degrees unknown sunlight exposure...
I read the older threads on this and I'm convinced this is not applicable to our pools. Chem geek mentioned that the group this represents has high bather loads that drive chlorine consumption much more than sunlight and the assumptions may fit their use patterns. Additionally there have been attempts to talk with the author further but the author has never responded.
I read the older threads on this and I'm convinced this is not applicable to our pools. Chem geek mentioned that the group this represents has high bather loads that drive chlorine consumption much more than sunlight and the assumptions may fit their use patterns. Additionally there have been attempts to talk with the author further but the author has never responded.
As an update, the pool has never been clearer, which only confirms that the pool service is not worth the money. What I had thought was clear before wasn't really clear at all. Its really amazingly clear now. I am hoping that I'll be able to keep it this clear myself using the BBB. I am concerned that that algae will come back given that he used algaecide and probably didn't shock the pool. I am firing the pool service as soon as my test kit arrives.
My test kit arrived. My numbers are:
CYA 100 (matching pool service and pool supply store). I ran the test at 1:2 and 1:3.
FC 8
CC 0
TA 100
pH 7.5
The pool store's readings a week a go were:
FC - 5
CC - 5
pH – 8
TA - 90
CH - 200
CYA – 99
According to the CYA/FC chart I have a target of 12, which means that I need to add a 96 oz of bleach, right? The pool service came out and dosed my pool with algaecide and a floc. The result is that my pool is crystal. Of course I am firing them because in 18 months of service this is the first time my pool looked good. I had actually forgotten what a crystal pool looked like so I wasn't even aware that I was getting the shaft.
I know that the advice is to drain the pool part way to reduce CYA to 50 or so. I am wondering though whether I should do it now, while the pool looks so good and during the swimming season (which continues here into Oct) or wait until the end of the season. Either way I'll do the chemicals myself so I hope it won't get green again. Thoughts?
CYA 100 (matching pool service and pool supply store). I ran the test at 1:2 and 1:3.
FC 8
CC 0
TA 100
pH 7.5
The pool store's readings a week a go were:
FC - 5
CC - 5
pH – 8
TA - 90
CH - 200
CYA – 99
According to the CYA/FC chart I have a target of 12, which means that I need to add a 96 oz of bleach, right? The pool service came out and dosed my pool with algaecide and a floc. The result is that my pool is crystal. Of course I am firing them because in 18 months of service this is the first time my pool looked good. I had actually forgotten what a crystal pool looked like so I wasn't even aware that I was getting the shaft.
I know that the advice is to drain the pool part way to reduce CYA to 50 or so. I am wondering though whether I should do it now, while the pool looks so good and during the swimming season (which continues here into Oct) or wait until the end of the season. Either way I'll do the chemicals myself so I hope it won't get green again. Thoughts?
safest would be to replace the water.
Just because it looks clear does not mean there is not algae still in it. Do an OCLT to confirm.
Remember that the pH test is but valid when FC is over 10ppm. So if you do not drain, you will have to be careful when checking the pH.
Posted from my Droid with Tapatalk ... sorry if my response is short
Just because it looks clear does not mean there is not algae still in it. Do an OCLT to confirm.
Remember that the pH test is but valid when FC is over 10ppm. So if you do not drain, you will have to be careful when checking the pH.
Posted from my Droid with Tapatalk ... sorry if my response is short
Just so you know, there's no way that in full sunlight even with a CYA of 100 ppm that a pool service could visit only every other week and have chlorine in the pool unless they were 1) using algicides or phosphate removers or 2) using Trichlor tabs/pucks or some other source of chlorine between visits. At best, some services can visit weekly with a CYA of 100 ppm where they can dose up to around 14 ppm or so and come back in a week with the FC down to around 4 ppm or so. Though the last couple of days have the FC below recommended levels, the high FC target kills off anything nascent that has started to grow.
As for the PPOA, ignore what they write since some of it is accurate and some of it is not, partly because their focus is for high bather-load commercial/public pools. Their charts on how CYA protects chlorine are wrong and we've seen how higher CYA levels definitely lower chlorine loss from sunlight, even with proportionately higher FC levels. It's just that it's harder to shock such pools if they run into problems which is why we normally don't recommend such high CYA levels except for pools with saltwater chlorine generators or others with more automated dosing.
As for the PPOA, ignore what they write since some of it is accurate and some of it is not, partly because their focus is for high bather-load commercial/public pools. Their charts on how CYA protects chlorine are wrong and we've seen how higher CYA levels definitely lower chlorine loss from sunlight, even with proportionately higher FC levels. It's just that it's harder to shock such pools if they run into problems which is why we normally don't recommend such high CYA levels except for pools with saltwater chlorine generators or others with more automated dosing.
Thanks chemgeek. That is why I am firing them. There methold marginally worked under perfect condition but broke down completely during the long heat spell we had here in Fresno. They are fired and gone. I am BBB at this point. I tested the pool at 8 FC yesterday evening and added 96 oz 6% bleach. Pool calculator predicts that 96 oz will raise my pool 4.6 to 12.6. I tested twice today at 14 and 14.5 (I think it second reading was really 14 because an extra drop sneaked in).
Should I conclude that my pool is really a bit smaller than 10000 gal? That the chlorine was stronger than 6%?
What is the formula for calculating change in FC as a function of pool volume and 6% bleach. I'd like to solve it for pool volume and see if that provides a better estimate than the one based on diminisions (because I have an irregularly shaped pool).
I will do the overnight test tonight to see if algae still lurks in the pool.
Thank you! I really appreciate the support of this community.
Should I conclude that my pool is really a bit smaller than 10000 gal? That the chlorine was stronger than 6%?
What is the formula for calculating change in FC as a function of pool volume and 6% bleach. I'd like to solve it for pool volume and see if that provides a better estimate than the one based on diminisions (because I have an irregularly shaped pool).
I will do the overnight test tonight to see if algae still lurks in the pool.
Thank you! I really appreciate the support of this community.
It's hard to know if the error is in the pool volume or the concentration of bleach or in testing (including dropper tip opening size, calibration of sample tube, concentration of FAS-DPD reagent, etc.). I would say that if you get fairly consistent results using different bottles of 6% bleach, especially different brands or sources, then your pool volume might be a little smaller than you originally assumed. You're talking about a 15% difference so not huge, but something you can just look at over time, especially when you replace test kit reagents at some point.