Welcome and yet another CYA/FC question.

[BryRocket]

Hello Y'all,

First post and new to the forum and new to maintaining a pool. I have read a couple books and spent a decent amount of time pursuing various forums and blogs. I'd say at this stage I've gathered about equal parts knowledge and confusion over some maintenance methods.

A quick summary of where I am and where I've been: Just had a 15' x 29' x 5.5' pool completed. It does have a large shallow tanning ledge so the total gallonage is roughly 13,500. Use a cartridge filter, UV lamp, VS Pump, in-line puck cholrinator, has two skimmers (independent), two drains (combined) and some bubblers. Pebbletech plaster. Pool was initially filled about June 1 2021.

During some COVID-crazed rumor/actuality, my wife saw on TV that CL could be in short demand this year and she was not going to get our pool time affected by lack therof so she went and bought 3 massive buckets of 3" tablets. We obviously started just sticking in about 5-6 of those in the cholrinator, turning it up to 3-4 and letting it do it's thing. I really only checked the CL and pH for a few months and we just tried to enjoy the water.

I eventually started to notice my CYA levels rise and now know that is due to the excessive use of the pucks. After reading around I flipped to almost exclusive use of liquid CL, baking soda and muriatic acid. Now I feel like I'm constantly battling elevated pH and quickly diminishing CL. The pool is crystal clear, no issues at all.

One of the main questions I have is about CYA, its effect on the CL effectiveness, and safety of CL at particular levels. I'll start by breaking down my readings from this afternoon from a test at Leslie Pools. FWIW, I rarely test there but was just curious about some of the things I don't test for.

FC: 2.65
TC: 2.66
pH: 7.8
TA: 105 (adjusted due to CYA), I got 140 on my own test.
***(On the TA, FWIW, this number has been about 40pts lower up until today, added a bunch of BS last night)***
CH: 304
CYA: 74
Iron: 0
Copper: 0.1
Phosp: 767
TDS: 900

So, I have read about all the pros and cons of the liquid CL vs puck debate but am starting to think maybe just a blend of each is best?? The pucks tend to keep the FC from tanking quite so quickly, make it a bit easier to regulate the pH. The liquid doesn't add excessive CYA, but doesn't seem to last all that long and raises pH some and contributes to the TDS ( I believe).

Back to the question: for my level of CYA, and if using the target of 7.5%, I get that my target CL should be ~5.5ppm. I have also read that you don't want to swim in water that has a CL level above 5ppm. So, this is confounding. Do I HAVE to drain/dilute this out to get my CYA level low enough (~40) that I can keep CL around 3ppm and have a "safe" pool?

At what point to people recommend "fixing" the elevated CYA levels?

Currently, I can add enough liquid CL per PoolMath to pull my CL from say 1 to 5 in the evening, but if people are all swimming the next day it will be back to 1, if not lower that next evening.

I'm just trying to decide how much I should really be worried about the CYA levels, how to best keep CL high enough to be effective but also low enough to be safe.

With regards to the pH I usually just lower it to a target of 7.2 in the evening and it is about 7.4 the next morning. 2 days later it'll be closer to 7.8-7.9ish and I retreat with a little MA to the target. I've heard that new plaster pools will create a bit of a battle there for a few months so I'm not too worried at this stage. Does that sound right?

Thanks in advance, sorry for the lengthy post. Hope you can filter through all that bs and find the question.

Bryan

 

[BryRocket]

Oh and just one more tidbit, my pool is in full sun, all day.

 

[BryRocket]

And one more thing that has confused me, when I measure my TA with either of my 2 test kits I get closer to 140. Is that the value I should always use in PoolMath and should care about or do I convert that based on my CYA levels?

Thanks again y’all. I hope to one day be on the other end of discussions like this.

 

[PoolStored]

Hello Y'all,

UV lamp, in-line puck cholrinator,

I would remove the UV and the Puck Chlorinator. There is no need for UV in an outdoor pool, it gets plenty of UV, all it does is consume your FC with the UV. You will get plenty of sanitation with the Chlorine. I would go to liquid Chlorine (more later) or go to an SWG pool.

I eventually started to notice my CYA levels rise and now know that is due to the excessive use of the pucks. After reading around I flipped to almost exclusive use of liquid CL, baking soda and muriatic acid. Now I feel like I'm constantly battling elevated pH and quickly diminishing CL. The pool is crystal clear, no issues at all.

One of the main questions I have is about CYA, its effect on the CL effectiveness, and safety of CL at particular levels. I'll start by breaking down my readings from this afternoon from a test at Leslie Pools. FWIW, I rarely test there but was just curious about some of the things I don't test for.

FC: 2.65
TC: 2.66
pH: 7.8
TA: 105 (adjusted due to CYA), I got 140 on my own test.
***(On the TA, FWIW, this number has been about 40pts lower up until today, added a bunch of BS last night)***
CH: 304
CYA: 74
Iron: 0
Copper: 0.1
Phosp: 767
TDS: 900

So, I have read about all the pros and cons of the liquid CL vs puck debate but am starting to think maybe just a blend of each is best?? The pucks tend to keep the FC from tanking quite so quickly, make it a bit easier to regulate the pH. The liquid doesn't add excessive CYA, but doesn't seem to last all that long and raises pH some and contributes to the TDS ( I believe).

Liquid Chlorine contains no CYA. You need to read this -->FC/CYA Levels At your CYA, which is 80 for our purposes, you need to MAINTAIN 9-11ppm FC to have enough sanitizing effect to stave of algae. And never let it get below 6.

Back to the question: for my level of CYA, and if using the target of 7.5%, I get that my target CL should be ~5.5ppm. I have also read that you don't want to swim in water that has a CL level above 5ppm. So, this is confounding. Do I HAVE to drain/dilute this out to get my CYA level low enough (~40) that I can keep CL around 3ppm and have a "safe" pool?

the 7.5% is an ABSOLUTE MINIMUM and at that point your are flirting with Algae. Your pool will be "safe" at 9-11, because it is balanced with your CYA level. You will not smell it, it will not irritate. It is where you need to be with CYA of 80. I also would not trust the pool store numbers until you get a good test kit. (see below). I think you would be reasonably safe to get your FC to 7-8 and keep it there until you get a good test kit.

You don't HAVE to drain/dilute, but the pool will be much more manageable. I suggest you download PoolMath to your smartphone. Configure your pool. It will tell you how much to drain to get your CYA to a certain target. To get to 40%, you will likely have to drain about 50% of the pool. Here is a good read on draining --> Draining

At what point to people recommend "fixing" the elevated CYA levels?

About where you are at for a non SWG pool. Any level above 70 makes it harder to manage and to SLAM if you have/get algae. SLAM Process

Currently, I can add enough liquid CL per PoolMath to pull my CL from say 1 to 5 in the evening, but if people are all swimming the next day it will be back to 1, if not lower that next evening.

You need to be at 9-11 for your CYA level. I have to add up to a gallon a day with sun and swimming. If I know it will be hot and sunny with swimmers, I may add chlorine during the day so my pool never get to the minimum for my CYA level.

I'm just trying to decide how much I should really be worried about the CYA levels, how to best keep CL high enough to be effective but also low enough to be safe.

Read above.

With regards to the pH I usually just lower it to a target of 7.2 in the evening and it is about 7.4 the next morning. 2 days later it'll be closer to 7.8-7.9ish and I retreat with a little MA to the target. I've heard that new plaster pools will create a bit of a battle there for a few months so I'm not too worried at this stage. Does that sound right?

I don't have plaster pool experience, and your pH issues are likely related to that and others will chime in.

Thanks in advance, sorry for the lengthy post. Hope you can filter through all that bs and find the question.

Bryan

All good. Final recommendation is to stop having the pool store test your pool. The test are many times inaccurate and inconsistent. Many times, the advice from the pool store is wrong on how to fix. Ask me why I chose my username. You can do testing at home. Get one of these kits, Test Kits Compared and get pool math. Bring your numbers here and we will continue to help.

 

[Bperry]

have also read that you don't want to swim in water that has a CL level above 5ppm.

That would be a rule for a pool with 0 CYA. Those recommendations are very old and only apply when not using CYA to buffer the chlorine. If you follow the CYA chart, it’s plenty fine to swim up to the SLAM level of chlorine for whatever CYA you have in the water. We had some friends over this weekend and swam with the FC at 17ppm as I’m coming down off a SLAM.

Also like mentioned above, the UV system breaks down chlorine in the water making it so that you need even more chlorine to keep the water clean. So I’d turn it off. If your pool is in the sun all day, the water is getting tons of UV on it which is why the chlorine breaks down in the sun (and why CYA is added to help reduce the amount of breakdown the sun does to it.

 

[BryRocket]

@PoolStored Thank you so much for taking the time to answer some of my questions. I truly appreciate it.

I would remove the UV and the Puck Chlorinator. There is no need for UV in an outdoor pool, it gets plenty of UV, all it does is consume your FC with the UV. You will get plenty of sanitation with the Chlorine. I would go to liquid Chlorine (more later) or go to an SWG pool.

Would the puck cholrinator not come in handy when on vacation? This touches on another question: What do y'all do when unable to attend to your pool for a few days? I've been exclusively using bleach but it really has to be added every day to every-other day?

On the UV, I use a 240v Paramount Ultra UV2. The requirements are 20min/80max GPM to achieve "desired sanitation". My VS pump runs a 30gpm from ~7am-7pm with it kicking up to 60gpm from 12p-5pm. This two lamp filter operates at 253.7nm (UV-C) which is great at killing crypto, giardia, algae, etc. but doesn't reduce FC. HOCl destruction primarily happens at 295nm (UV-B). Our atmosphere absorbs UV-C so we primarily get lots of UV-A and some UV-B here at our pool level. So, yes, the sun UV does reduce our HOCl (which our bank accounts are well aware of) but isn't a great disinfectant. The UV-C wavelength that these pool filters use are great at the disinfecting but thankfully not detrimental to our FC.

You will not smell it, it will not irritate. It is where you need to be with CYA of 80.

Good to know.

I also would not trust the pool store numbers until you get a good test kit. (see below). I think you would be reasonably safe to get your FC to 7-8 and keep it there until you get a good test kit.

I do have a good test kit and use it almost exclusively. I sometimes will get that water tested there just to see what their CYA number says. I'm not SUPER confident in my Taylor CYA test. Can I still see the black dot???

I suggest you download PoolMath to your smartphone. Configure your pool. It will tell you how much to drain to get your CYA to a certain target.

I do have the paid version of POOLMATH but I can't see where it will give me some dilution calculator for CYA?

I have to add up to a gallon a day with sun and swimming.

YIKES! This is gonna get real expensive huh? Also, I'm just not around every day. Gonna have to find a solution here. I'm hoping that if I add a little algecide and keep the UV filter going it may help with some of the drops in attention.

I don't have plaster pool experience, and your pH issues are likely related to that and others will chime in.

Since lowering my TA down a little it appears my pH is holding a little better. Also I turned my bubblers schedule off so now we just turn them on when we want them and they don't run all day. Seems to have maybe helped.

All good.

Thanks man.

 

[mknauss]

The UV-C wavelength that these pool filters use are great at the disinfecting but thankfully not detrimental to our FC.

UV Systems - Further Reading

www.troublefreepool.com

 

[BryRocket]

Thank you @Bperry for your contribution. I'm much relieved to know about the safety of FC levels with CYA. This was something that was really bothering me and I feel relaxed about it now.

Also like mentioned above, the UV system breaks down chlorine in the water making it so that you need even more chlorine to keep the water clean. So I’d turn it off. If your pool is in the sun all day, the water is getting tons of UV on it which is why the chlorine breaks down in the sun (and why CYA is added to help reduce the amount of breakdown the sun does to it.

I replied above on this but in short, from what I know/read about UV and on these filters (mine anyway), they do not reduce FC levels.

BUT! For my own experiment, I'm going to check the FC in the pool at night, let the pump + UV run all night and then recheck the FC in the morning. I'll redo the experiment but turn the UV off and see if there is anything significant to note.

Thanks again.

 

[BryRocket]

UV Systems - Further Reading

www.troublefreepool.com

Thanks @mknauss. Solid info link. I'm not sure if I'd purchase and install one of these now but since I have it already I think I'll be keeping it running. If it isn't removing FC, seems like it couldn't hurt.

 

[BryRocket]

Do you recommend using the actual tested TA number for PoolMath from my kit or do you recommend adjusting that for the CYA levels?

Also, any advice on Taylor CYA testing appreciated. I feel like there is a range between when I think the black dot isn't visible to when I really know it isn't visible. Does the lighting make a big difference? I have enough reagent to do another test and want to redo it so I have a better idea of where I am.

 

[Bperry]

Thanks @mknauss. Solid info link. I'm not sure if I'd purchase and install one of these now but since I have it already I think I'll be keeping it running. If it isn't removing FC, seems like it couldn't hurt.

If you read to the end, it mentions that it does convert some of the chlorine, evidently just not enough to be significant. I’m kinda curious now what “significant” means over long term use. Interesting article anyway.

 

[Bperry]

Do you recommend using the actual tested TA number for PoolMath from my kit or do you recommend adjusting that for the CYA levels?

Also, any advice on Taylor CYA testing appreciated. I feel like there is a range between when I think the black dot isn't visible to when I really know it isn't visible. Does the lighting make a big difference? I have enough reagent to do another test and want to redo it so I have a better idea of where I am.

You enter the actual number in poolmath. Pool math does all the adjustments.

I’ve found the CYA test better with my back to the sun, with the vial on a stable surface, and look down the tube from about 18” away. I got some of the test standard and the dot was not completely blocked, but ~95%. I usually fill I’m the tube up in 10ppm increments until I really can’t see the dot, then record the number at the previous (higher number)

 

[PoolStored]

@PoolStored Thank you so much for taking the time to answer some of my questions. I truly appreciate it.

Happy to help.

Would the puck cholrinator not come in handy when on vacation? This touches on another question: What do y'all do when unable to attend to your pool for a few days? I've been exclusively using bleach but it really has to be added every day to every-other day?

Sure! Lots of people do that. If you understand what the puck adds in CYA and cover it with your FC, great solution!

I have a stenner pump with a bleach vat that injects chlorine to my plumbing. Search Stenner Pump here, lots of info. I connected to smart plug controlled by alexa. I test, calculate number of minutes in my head for my pump, then say "Alexa run pump for 30 minutes." I'm done. I know my pool well enough that when I go away I just setup alexa routine to pump for 30 minutes and it will maintain my pool.

On the UV, I use a 240v Paramount Ultra UV2. The requirements are 20min/80max GPM to achieve "desired sanitation". My VS pump runs a 30gpm from ~7am-7pm with it kicking up to 60gpm from 12p-5pm. This two lamp filter operates at 253.7nm (UV-C) which is great at killing crypto, giardia, algae, etc. but doesn't reduce FC. HOCl destruction primarily happens at 295nm (UV-B). Our atmosphere absorbs UV-C so we primarily get lots of UV-A and some UV-B here at our pool level. So, yes, the sun UV does reduce our HOCl (which our bank accounts are well aware of) but isn't a great disinfectant. The UV-C wavelength that these pool filters use are great at the disinfecting but thankfully not detrimental to our FC.

UV-C absolutely positively degrades both hypochlorous acid and hypochlorite ion as shown in Figure 3 of the paper Photolysis of aqueous free chlorine species (HOCl and OCl-) with 254 nm ultraviolet light where you can plainly see significant absorption in the 200-250 nm range though it is not as high as the absorption for hypochlorite ion in the 270-330 nm range (the UV in sunlight that reaches the ground starts at around 300 nm and up). The quantum yield is about 1 which means that the absorption results in breakdown of the molecule. So if you believe "thankfully not detrimental", then you should question the accuracy of the other claims you may have heard.

Good to know.


I do have a good test kit and use it almost exclusively. I sometimes will get that water tested there just to see what their CYA number says. I'm not SUPER confident in my Taylor CYA test. Can I still see the black dot???


I do have the paid version of POOLMATH but I can't see where it will give me some dilution calculator for CYA?

Best thing I ever did was to buy a 50ppm standard and ran the test. With it, I new what the black dot was supposed to look like. TFTest CYA Standard

I can't find it in pool math either. I could swear I used it in Pool Math when I did my replacement. Maybe @mknauss knows and can refresh me. Either way, you can go here, scroll to CYA put in your CYA and your target, it will tell you how much water to replace.
Old Calculator

YIKES! This is gonna get real expensive huh? Also, I'm just not around every day. Gonna have to find a solution here. I'm hoping that if I add a little algecide and keep the UV filter going it may help with some of the drops in attention.


Since lowering my TA down a little it appears my pH is holding a little better. Also I turned my bubblers schedule off so now we just turn them on when we want them and they don't run all day. Seems to have maybe helped.


Thanks man.

Make sure any algecide you use doesn't contain copper/metals.

 

[mknauss]

Do you recommend using the actual tested TA number for PoolMath from my kit or do you recommend adjusting that for the CYA levels?

Poolmath uses the tested TA level. Any need for adjustment is done within Poolmath.

Also, any advice on Taylor CYA testing appreciated. I feel like there is a range between when I think the black dot isn't visible to when I really know it isn't visible. Does the lighting make a big difference? I have enough reagent to do another test and want to redo it so I have a better idea of where I am.

For the CYA test, it should be done in bright sunlight, back to the sun, vial at waist, etc.
Once you have your solution ready, back to the sun, etc. Fill the vial to a line, say 80, lower the vial to your waist level and glance for the dot, you see it, add solution to the 70 line, glance, see it, repeat until you no longer see it with a glance. Then use the CYA value one step above the line you read. So if you stopped at 50, use 60 ppm CYA.

The vial is in logarithmic scale. So it is not viable to interpolate between the lines. Just use the whole numbers, such as 50, 40, 30, ....

 

[mknauss]

I can't find it in pool math either. I could swear I used it in Pool Math when I did my replacement. Maybe @mknauss knows and can refresh me. Either way, you can go here, scroll to CYA put in your CYA and your target, it will tell you how much water to replace.

It is a straight ratio. If you need to lower your CYA by 50%, you need to drain and refill 50% of your pool volume.

 

[PoolStored]

It is a straight ratio. If you need to lower your CYA by 50%, you need to drain and refill 50% of your pool volume.

I know that, and thought about just saying that, but the calculator is so much more fun! I'll do that next time. I still could swear I saw it in pool math. Maybe a simple upgrade to the app to suggest draining %?

 

[Donldson]

I’m kinda curious now what “significant” means over long term use.

The reason it's not a major contributor to chlorine loss is (brace yourself) because residential UV systems are so horribly under powered that they don't actually do much anyway.

The thing about them is that while the concepts are solid (UV-C kills pathogens, no argument there) the implementation in residential pools is nothing but a cash cow. If a pool is properly chlorinated then the chlorine in the bulk of the water kills off pathogens long before they have the opportunity to be exposed to the UV-C in the filter system. So all it is really doing is burning off chlorine. Except the UV-C output is so low that it doesn't really do much of that either. But it is outputting UV-C... initially. These bulbs have a fairly short lifespan in which they emit UV-C so they need regular replacement. Regular replacement that creates a nice residual income for pool stores.

And that is why pool builders push their inclusion, even to the point of including them below cost or even free. Anything that needs regular replacement of components is much beloved in the industry, while things that rarely need replacements (SWGs) are often talked down. UV systems, ozone systems, mineral systems, these things never save the pool owner money versus straight chlorine use. They only make sure the money spent is directed towards the right people.

 

[PoolStored]

Thanks @mknauss. Solid info link. I'm not sure if I'd purchase and install one of these now but since I have it already I think I'll be keeping it running. If it isn't removing FC, seems like it couldn't hurt.

Nah, won't hurt. But likely doesn't help much, if at all.

The requirements are 20min/80max GPM to achieve "desired sanitation". My VS pump runs a 30gpm from ~7am-7pm with it kicking up to 60gpm from 12p-5pm. This two lamp filter operates at 253.7nm (UV-C) which is great at killing crypto, giardia, algae, etc. but doesn't reduce FC. HOCl destruction primarily happens at 295nm (UV-B). Our atmosphere absorbs UV-C so we primarily get lots of UV-A and some UV-B here at our pool level.

This *sounds* like marketing cut and paste. Crypto, giardia are exceedingly rare in residential pools. Both are associated primarily with fecal matter. If you have good hygiene, and are aware of unpotty trained children, the likelihood of these pathogens are essentially zero. UV will not kill algae or anything else on your pool walls. I had a "Pool Store" sell me a new unit. After I did the research, I tore mine out. Wasn't worth the $$ for the electricity. Anyone want to buy a new Delta UV?

 

[proavia]

If you only have the K-2005 Taylor test kit, you are missing the all important FAS-DPD test. The FAS-DPD test is the most reliable for FC levels - espedially above FC 5 ppm.

If you look at the price of the K-1515C (FAS-DPD) test kit and 8 or more ounces of the CYA (R-0013) reagent, it may be more cost effective to just order an entire TF-100 testkit and have all the additional reagents too. If you don't already have the SpeedStir (or equivelant), consider getting that also as it will make your testing easier, faster and the results more consistent.

As for the CYA test, do NOT stare while looking to see if the black dot is visible or not. After mixing the testing solution, add to the first line and GLANCE to see the dot. If visivle, add to next line, etc. Once the dot is NOT visible when glancing, take that number and round up to the next whole graduation.... if the dot is visible at 50 but isn't visible at 40, round the CYA reading up to 50 and dose FC accordingly using the FC/CYA Levels.

Don't "adjust" any test results from your own test kit. Just enter it into PoolMath. PoolMath will make any necessary adjustments automatically.

Your UV device is NOT a filter. Only a small portion of your entire pool volume ever goes thru the UV device. No way can it ever "santize" your entire pool. And it provides absolutely zero residual sanitation either. If you want to believe it works, that's up to you. But you still need to keep the FC at the levels recommended for your CYA as shown in the FC/CYA Levels to insure proper sanitation of your pool water.

If you are unable to attend to your pool's FC needs daily or ever other dayconsistently, consider adding a SWG.

 

[PoolStored]

By the way, if you have an "accident" in your pool, guidance is to raise and maintain FC to 10ppm for 26 hours. You can do 20ppm for 9 hours, but depending on your CYA may hurt your vinyl liner. This achieves a 4 Log (99.99%) reduction of oocysts. (Oh, and remove the accident by filtering to WASTE).

Kebabjian, Richard S. “Disinfection of Public Pools and Management of Fecal Accidents.” Journal of Environmental Health, vol. 58, no. 1, 1995, pp. 8–12.