CYA off the scale

[twilson]

My pool (see signature) is 6.5 years old and has never been drained. For most of its life, I've maintained chlorine levels using trichlor tabs in the skimmer and broadcast dichlor to shock. Recently, it's been harder to maintain adequate levels, and I've had problems keeping algae away. Exasperated, I looked around the Internet, found the Pool School, and read everything there. Now I think I understand the problem much better. I got a good testing kit, and found that CYA was (not surprisingly, given my previous method of chlorination) off the scale: the scale is logarithmic, and I estimate by extrapolation that it's around 160. Around the same time, a friend of mine in the pool business had his maintenance guy come by to check things out for me as well. He tested the phosphates and found them to be very high. He put in a bottle of phosphate remover, told me to run the filter overnight and clean it the next day, which resulted in lots of blue cloudy water coming out of the cartridges during cleaning. He didn't seem to understand what was wrong with high CYA, and said that many of the pools he services have high CYA without problems.

Last night, early evening, my test results were:

FC: 1.2
CC: 0.2
pH: 7.4
ALK: 140
CH : 310
CYA: 160 (est.)

I was never told the volume of my pool, so after this last test, I added 2 gal of 10% bleach, ran the filter in the dark for several hours, and retested FC at 10.6 (CC still 0.2). From this, I calculated a pool volume of 22K gal. This morning, before the sun hit the pool, FC was 9.2 and CC was 0.

So, here are my questions:

1. It seems clear that I need to drain the pool, but it's too hot for that now (or so I've been told). City codes allow homeowners to drain their pools more frequently than the required three years if CYA is over 100 (or TDS is over 2500, or CH is over 450), but there don't seem to be any regulations about maximum CYA. Is the pool safe enough to swim in? If so, what's my best course of action to keep the pool in swimmable condition until the late fall/early winter? The Chlorine/CYA chart seems to require possibly dangerous levels of chlorine (on top of the already high CYA level) for sanitation.

2. Is the phosphates level something that I should regularly test for and correct, as the pool guy seemed to suggest? From what I've read here, it seems little more than a cash cow for the pool industry -- although what the service guy said about it being a problem made some sense.

Thanks!

 

[JohnT]

Welcome to TFP.

The key thing to understand about the Chlorine/CYA relationship is that the high CYA makes those high chlorine levels effectively very low. CYA binds with some of the chlorine, making it inactive until the unbound chlorine begins to be consume by sunlight or in the sanitation process. The 12ppm FC at 100ppm CYA is the same as the 3ppm FC at 20ppm CYA as far as oxidizing action. You won't smell a strong chlorine smell and it won't burn your eyes or fade your bathing suit.

 

[anonapersona]

He didn't seem to understand what was wrong with high CYA, and said that many of the pools he services have high CYA without problems.

From what I've read here, it seems little more than a cash cow for the pool industry -- although what the service guy said about it being a problem made some sense.

Thanks!

I think the issue is "problem for who?". They guy getting paid to deal with it figures "No problem" add this, add that, get paid. The pool owner who is told that this is normal operation just starts to think that pools themselves are problems, not knowing that it is the out of control CYA that is the key.

Bravo on the pool volume work. Well done.

Sounds like you are in the clear with draining some water to adjust CYA. We sometimes hear of pools that began at say 150 then drain 50% and see the next test at 90 instead of the expected 75 so your comment of an exponential scale makes sense to me there. I should have noticed the scale on the CYA test cylinder to see that myself.

Based on that, you ought to be able to calculate how much needs to be drained to get back into the "40 +/- 10" range. Take into account water table if this is an inground pool.

As for safe swimming, you need to be keeping the pool at FC 12 ppm for a minimum based on the Chlorine/CYA chart http://www.troublefreepool.com/pool-school/chlorine_cya_chart_shock suing twice the values for CYA 80. Since you are having such trouble keeping any chlorine, you probably need to shock and that gets expensive since you need FC of 62 to do that, and you need to stay there for a few days probably. Really, if they will allow you to, you ought to drain and refill to reduce to at least maybe 50 if not 30 or 40. Way cheaper for chemicals. Otherwise, I just doubt the pool is sanitary. But, let's hear from the pros here, they will be along soon.

 

[sbluhm]

1. It seems clear that I need to drain the pool, but it's too hot for that now (or so I've been told). City codes allow homeowners to drain their pools more frequently than the required three years if CYA is over 100 (or TDS is over 2500, or CH is over 450), but there don't seem to be any regulations about maximum CYA.
I don't understand why the temperature would matter in terms of draining the pool? It seems like most folks just do partial drains to shed CYA. If you had a DE filter, would you be allowed to backwash? Maybe you could do a series of "backwashes" over the next months to slowly bring CYA in line? It seems like a lot of folks, even in the pool industry, have never heard of the CYA/Chlorine relationship... and hence there is lots of advice about "shock weekly", etc. Maybe your pool guy always shocks pools when he visits, or he works with a lot of SWG's that tolerate higher CYA.

2. Is the phosphates level something that I should regularly test for and correct, as the pool guy seemed to suggest? From what I've read here, it seems little more than a cash cow for the pool industry -- although what the service guy said about it being a problem made some sense.
This question is still debated on this board, but the overriding advice seems to be don't worry about it, that if you focus on maintaining proper chlorine levels it won't be an issue. Sounds good to me considering how expensive phosphate remover is!

If you haven't already been told, you'll want to get a good test kit so you can monitor accurately and consistently your chlorine, PH, TA and CYA.

Good luck!

 

[frustratedpoolmom]

Is your pool free-form? Dimensions would help you calculate the gallonage better. Do you have any records indicating the size?

My reasoning is often the stronger concentrations of chlorine have lost some of their strength, so that 10% might not have been 10%. Also there is the possibility that some of the FC could have been consumed immediately if there were nascent algae present, your FC residual may not be the indicator of the size as close as you guestimate....

Phosphates are algae food, but if you maintain the FC levels according to the CYA chart - they are a non issue.

I would do a series of partial drains, perhaps to the bottom of the skimmer and then repeat until the CYA is at the very least 70. If temp concerns regarding your finish, rent a sumbersible pump and try to complete the drains/refills in the evening/nighttime hours when no sun is hitting the surface. Draining 1/3 at a time is usually safe for most pools, it's not exposed for that long...

 

[twilson]

Is your pool free-form? Dimensions would help you calculate the gallonage better. Do you have any records indicating the size?

Yes, it is free-form -- not curved, but round planters at the corners and along one of the long sides, many steps of different depths, a few different widths, etc. The contractor didn't provide a volume, maybe because it was too hard to calculate! I tried computing volume by breaking the pool into sections and guessing average widths and depths for each section, and I get figures that are in the same ballpark, maybe a little higher (up to about 24K). The pool guy I mentioned in my original post estimated 30K by sight, but I think the complicated geometry threw him off.

My reasoning is often the stronger concentrations of chlorine have lost some of their strength, so that 10% might not have been 10%. Also there is the possibility that some of the FC could have been consumed immediately if there were nascent algae present, your FC residual may not be the indicator of the size as close as you guestimate....

Yes, that may be possible. I get my liquid chlorine from Home Depot, and I appreciate that it is not always kept in the best conditions, or freshly shipped in. It would be interesting to have it tested once in a while to see what the effective percentage of chlorine is. I guess it's possible that the bleach from a pool store might be a better value, even though it is more expensive.

 

[PaulR]

Re. pool volume: If you want to measure it chemically, use Clorox from a grocery store or big-box store; it turns over fast enough, is kept at reasonable temperatures, and 6% degrades very very slowly. So you can trust that it really is 6%. 1 gallon of 6% bleach in 10,000 gallons will raise FC by 6; in your pool I'd add two gallons and see where it got to. Note that's gallons, not jugs. This works best if you don't have an algae bloom in progress, of course.

Re. CYA: You can dilute pool water 50/50 with tap water and test CYA of the result, to double the range of the test. That will tell you whether "over 100" means 120 or 180.
--paulr

 

[twilson]

Re: CYA off the scale (REALLY off!)

Re. CYA: You can dilute pool water 50/50 with tap water and test CYA of the result, to double the range of the test. That will tell you whether "over 100" means 120 or 180.
--paulr

I tried a 50/50 dilution, and the CYA was still off the scale. So I just tried it again with a 25/75 dilution, and got a reading of 100ppm. Therefore the CYA in my pool right now is 400 ppm! Just so readers don't think I'm making a mistake here, let me detail the test.

I filled a test bottle with pool water, collected from about 2ft below the surface. I filled a graduated cylinder with 20ml of the pool water, and added tap water up to 80ml. I mixed for a little while, then I poured 7ml of the solution into the test bottle that came with my kit (Leslie's FAS-DPD Complete) and added 7ml of Cyanuric Acid Reagent (Taylor's R-0013), bringing it up to the 14ml mark. I then capped and mixed for 30 sec, and dripped the cloudy solution into the CYA comparator tube until I just was not able to make out any difference in brightness over the black dot and the rest of the bottom of the tube. The water in the tube was at the 100 mark.

So now I have new question: the considerable difficulties in maintaining sanitation with chlorine aside, is 400ppm of CYA dangerous to swimmers by itself?

As for draining the pool: is it better to get a professional service to drain and (steam? acid?) clean the pool, remove the calcium build-up at the waterline on the tiles, etc., or is this something that isn't too hard to do myself?

 

[frustratedpoolmom]

If you have staining/scale all over the pool service then yes, you should probably consider a professional service to do an acid wash - if it's just at the waterline that may be something you can handle yourself, by draining down a foot or so and then using a diluted acid solution to remove the scale... use the "google search" feature -bottom left for finding other threads about DIY acid washes.

You do lose some accuracy when doing dilution with testing - but it does sound like the CYA is very high. Just for a future note, mix the solution together for 30 seconds, let it set for a minute and then mix it again for another 30 seconds before you put the solution in the view tube.