How best to manage high CYA

[copster30]

Hi folks,

Just bought a new home which has an inground plaster pool, around 20k gallons. Tested the water and seeing high CYA. Previous home owner was using 3" chlorine tabs in a floater. How do you recommend i proceed? Should i remove this and start managing chlorine manually with clorox?

Following are levels

FC - 2.6
CC - 0.2
pH - 7.6
TA - 120
CH - 160
CYA - 100

Cheers,

Rob

 

[mas985]

It is possible to maintain a pool with a CYA level that high but the FC would need to be kept around 10 ppm to compensate. Otherwise, you could end up fighting an algae battle that would need a lot of chlorine to bring under control. But you will need to stop using the pucks and go with liquid chlorine.

 

[Jeetyet]

A CYA reading of 100 is at the top limit of what the test will read, so your level is probably much higher than that. How did you get these results? Pool store, or do you have your own kit? If the results are from the pool store the CYA test is the one they get wrong most often so its probably nowhere near correct.

IF the CYA reading is correct then you should drain at least half the water to lower it into the recommended range of 30 to 50. If you're doing your own testing then you should do a 50/50 dilution with pool water and tap water, do your test and double the results. That should get you closer to your actual level, and will tell you how much water you should drain.

Yes, stop using the pucks and switch to liquid chlorine/bleach. Save the pucks for when you will be away from the pool for a while and can't check/dose FC often. Since you have a plaster pool, and your CH level is lower than the recommended level of 250-350, if you wanted to you could use Cal-Hypo for a while as your chlorine source. When your CH came up to the recommended range you could then switch to liquid chlorine/bleach.

 

[copster30]

Thanks for the advice. I'm using the Taylor K-2006 to test. You have to pour in the CYA mixture until you can no longer see the dot at the bottom of the vial. It looked like it was around 90-100 so I'm hoping it's not way over 100.

 

[danacc]

Welcome!

This CYA test has a logarithmic scale, not linear, so it is hard to eyeball readings around and over 100. I recommend you re-do the test using the 1:1 dilution of pool water and tap water, then double the result as Jeetyet suggested. Your CYA level may very well be around 100; the way to know for sure is to do the diluted test and see if it confirms that reading or suggests a different value.

 

[Jeetyet]

I'd just go ahead with replacing about half the water and re-test when done. Whether or not you can do so all at once or should do several partial drain/refills would depend on the level of your ground water. If you have a high water table and drain too much at once you risk damaging the pool.

<edit>
If you have plenty of CYA test reagent then go ahead and re-test via the dilution method now to get a better idea of actual level to know how much to drain. If you're getting low on reagent, and since a CYA of 90 would still require a 50% drain, I'd probably just drain first and test later.

 

[mas985]

copster30,

Are you in an area where you will close your pool over the winter? You may find that CYA drops significantly over the winter.

Also, I find that CYA drops when the FC level is raised above shock levels. You would have to run the numbers but it could be more cost effective than refilling the pool.

 

[Patrick_B]

copster30,

Are you in an area where you will close your pool over the winter? You may find that CYA drops significantly over the winter.

Also, I find that CYA drops when the FC level is raised above shock levels. You would have to run the numbers but it could be more cost effective than refilling the pool.

Can you elaborate on this please? If this is common, I would love hearing more about it. How far above a SLAM level gets the cya down?

 

[copster30]

Thanks for the tip re the dilution method. Will do that.

I'm hoping not to have to drain since wouldn't even know where to begin with that process, but, oh well, learning as I go.


I'm in south florida so pool will run through the winter season.

 

[mas985]

copster30,

Are you in an area where you will close your pool over the winter? You may find that CYA drops significantly over the winter.

Also, I find that CYA drops when the FC level is raised above shock levels. You would have to run the numbers but it could be more cost effective than refilling the pool.

Can you elaborate on this please? If this is common, I would love hearing more about it. How far above a SLAM level gets the cya down?

This post explains the process: degradation-of-cyanuric-acid-cya-t8880.html

Eventually, CYA degrades at any level of FC it just degrades much faster at shock levels. So given enough time, the CYA should drop to acceptable levels but in the mean time, you would need to maintain the appropriate FC levels for the given CYA level.

 

[copster30]

So i did the tap and pool water test and it looks like my CYA is around 180-200 so i guess i'll have to look at draining.

Thanks for all the advice!

 

[Jeetyet]

So i did the tap and pool water test and it looks like my CYA is around 180-200 so i guess i'll have to look at draining.

Thanks for all the advice!

So your dilution result is still 90 to 100, basicly where you were to start with. If you have plenty of reagent, and want to play, you can do the half & half dilution like before, THEN dilute that solution with half tap water again. Perform your test and multiply result by 4.

As it is, given your results, you're looking at around at least a 75% drain to get CYA down to about 50. And thats assuming that CYA is not much higher than 200 which it very well could be. You can thank the stabilized chlorine pucks for your situation but at least you've found this forum and now know what causes these problems so you won't be subject to this happening again, once you get it all straightened out.

You might want to check with some pool builders or pool stores in your area, maybe even neighbors, to get some input on ground water levels in your location. If you could do so without risking damage to the pool you might want to consider just doing a complete drain and refill and start over. Of course you always have the option of doing partial drain/refills over an extended period, but, you'll have to monitor closely and maintain the recommended level of FC so as to avoid an algae problem. Otherwise getting rid of algae at a very high CYA level will require quite a lot of bleach.

In any case, don't panic and rush into anything quickly. Your pool didn't get this way overnight and the fix won't occur that quickly either. Take your time, educate yourself and explore your options, and as always I'm sure others here will have some further suggestions and options for you to consider.

 

[copster30]

Thanks Jeetyet. Much appreciated. Cheers