CYA level extremely high - need to drain / refill pool but have questions

PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
Hello all, my pool chemistry is out of whack and I would appreciate any advice.

Our CYA is 185 ppm with Free Chlorine of 27ppm. Our PH is also very low based on using a test strip and from the Leslie's pool store test, which yielded a PH of 6.4. I tried to test PH with our Taylor kit but the color value is yellow, and doesn't match any of the colors on the comparator tube so I couldn't get an exact value.

On one hand, I know I need to do a partial drain and refill of the pool due to the high CYA value. On the other hand, I'm a little concerned about doing that being that we are in the middle of a Texas summer and I worry that the high heat could damage any plaster that gets exposed in the draining process. According to the pool calculator the optimal FC range for this amount of CYA is 14-22 which we are not far from. Our water also looks great - it's not cloudy, it has no algae. So part of me wonders if I should add something to increase the PH so that the water isn't so acidic, and let the FC levels drop naturally until they're in the proper range for that level of CYA, and then drain / refill the pool in the September time frame when the temperatures start to go down. Ultimately my questions are:

1) Should I go ahead and drain the pool now, or should we maintain the recommended level of FC for this high of an amount of CYA and wait until temperatures fall to drain and refill so that there is less risk of damaging the plaster?

2) If we wait to drain the pool, would it be safe for swimming if we maintain the FC in the 14-22 ppm range and increase the PH to between 7.2 - 7.8?

Thanks in advance!
 

zea3

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Jul 10, 2009
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Houston, Texas
Hi, welcome to TFP! Yes please bring up the pH right away. If you are able to get enough chlorine to maintain the recommended FC levels you can wait until it is cooler to drain and refill. You will need to stay very diligent on maintaining the proper FC. If you let it drop too low your will get an algae bloom, and slamming the pool with a high CYA is difficult. You can also drain and refill in smaller increments until you can do a major water replacement in the fall. You can take advantage of any predicted heavy rains by draining a few inches and allowing rainwater to fill the pool. You never want to completely drain the pool dry without knowing where the water table is. The pool is safe to swim in up to slam levels of chlorine.
 
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PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
Thanks Zea! I tried to add 2 lbs. of baking soda last night to increase the pH, but it didn't make a noticeable difference and my phenol test still gave a yellow result this morning. It looks like I'll need to add borax or soda ash and I think in order to determine how much I need, I have to know alkalinity.

I found a couple of articles that indicated that CYA does effect total alkalinity and wondered whether I should adjust for that in the TA test somehow. One article indicated that when you have a high amount of CYA you should essentially calculate total (carbonate) alkalinity as:
TA ppm - (CYA ppm / 3) = C. (source - https://blog.orendatech.com/five-things-cyanuric-acid)

When I test my alkalinity with my Taylor kit, my TA is 100 ppm. If I apply the above formula, the result I come up with is 38 ppm TA: 100 TA ppm - (185 / 3). Which TA value should I use for purposes of determining what to add to my pool to fix pH / alkalinity issues?

Thank you for all your help!!
 

mknauss

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TFP Expert
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May 3, 2014
51,245
Laughlin, NV
Pool Size
6000
Surface
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Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Poolmath manages the TA adjustment.
If you are testing your TA at 100, your pH should not stay low too long.

How did you test a CYA of 185?
Also, a FC above 10 ppm messes with the pH test. So be ware of that.
 

PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
Hi Marty, I had the water tested at Leslie's and that's where I originally got the 185 ppm value. I was worried about my chemicals because the FC was high and not coming down, and I didn't understand why. I actually didn't even think CYA could be a problem because I haven't added any, plus I had been using these easy-to-use (and it turns out, inaccurate) test strips that showed low / no CYA in my water. I came home and used my Taylor test kit (which I should have been using all along) and sure enough, the Leslie's result for CYA was correct. My CYA was so high I had to dilute my sample and multiply my result by 2 when I tested it myself. Now I think that the reason my CYA was so high must be the tri-chor tabs we have been using.

I know that high chlorine does mess with some of the tests, but when I look at the technical FAQ for the Taylor pH test, it says phenol tests can turn purple or blue when sanitizer is high, and mine turns yellow. When Leslie's tested my water, they tested the pH at 6.4. They didn't even test alkalinity because they said the CYA was throwing it out of whack.

I wouldn't be surprised if my pH was very low because we have had a lot of rain down here, plus the tri-chlor tabs alone are supposed to be pretty high in pH.

The pool calculator is a bit confusing to me in this area because if I put a current value of 100 in the TA area, it tells me I need to add acid - which I think has to be wrong. If I go to the pH area and enter my current pH of 6.4 (using Leslie's value because I'm not getting meaningful results with my Taylor test kits, possibly due to other chemicals throwing it off) and a current TA of 100, it tells me to add 19 lbs of Borax. What I may do is go ahead and start with adding a 4lb box of Borax and see what the tests say after 24 hours. If anyone has any advice I'm all ears. Thanks so much! I truly appreciate this forum!!
 
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Newdude

Mod Squad
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Jun 16, 2019
18,139
NY
Run your own tests pronto. We’ve seen several this season of Leslies saying very high CYA when it was either fine ore slightly high.

Don’t drain your pool on a guess.
 

PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
Thanks New Dude, I did run my own CYA test with my Taylor 2006 test kit. It did confirm the result I got from Leslie. The black dot was totally obscured before the sample even reached the measurement indicators. I had to retest with a diluted sample and multiply my result by 2 which ended up at 180 (almost the same as Leslie).

Appreciate everybody's feedback!!
 
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Newdude

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I did run my own CYA test with my Taylor 2006 test …………. I had to retest with a diluted sample and multiply my result by 2 which ended up at 180
AWESOME!!! Now we know we like the results. Fire / drain away.
almost the same as Leslie
We’ve never said they can’t be right. The laws of infinite probably say they will be right at times too. One try out of a trillion. :ROFLMAO:

But seriously. Their results are just all over the place. No telling how off or if they are off today. Maybe they calibrated the machine the day before and starting next week it’s off for the remainder of the month. I want to make them do mine a couple of times when I get my pool built. I want to see if it claims the same thing 3 times in a row. With what I’ve seen here I even doubt they can repeat their own results.
 
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zea3

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Jul 10, 2009
14,440
Houston, Texas
Constant use of trichlor tablets has driven your pH extremely low. Add 1/2 of what Pool math says towards reaching a target of 7.4, let it mix with the pump running a couple of hours then test again. Keep in mind with poolmath if you enter a target value to lower TA it will tell you what to add to lower that value, however at this time you do not need to lower TA. If current TA test is 100 than also make 100 your target TA. That way you should not get any contrary information to raising pH.
 
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PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
yes.

Do raise the pH as it is low enough to damage things. But get your plan together to drain/exchange the entire pool volume.
Update - today these are my values:

pH - sitting at 7.6 (after adding quite a bit of Borax).
FC - 20 ppm (I have not added chlorine, but no one's been swimming in it so that's the only reason I can see why it's still so high).
CYA - 200 ppm. I took the tri-chlor tabs out days ago so there's no logical reason other than human error in testing that it could have gone up. This week I've been in a learning curve with the Taylor kit but finally feel like I'm getting the hang of using it so I'm more confident with my test result today than last time I tested.

Marty, you mentioned you think I should drain the pool right away instead of waiting until the end of the season and I wondered if you could share why you think that. I don't disagree that the water needs to be drained / exchanged, I'd just rather do it after the heat of summer. I'm still learning about all this and know enough to be dangerous, but my initial thoughts are that if I can maintain FC with liquid chlorine at around 7.5 % of the CYA, and if the pH is in balance, which it seems to be now, then it should be safe for swimming. Just trying to figure out if I've overlooked anything.

Thanks so much!!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
51,245
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I don't disagree that the water needs to be drained / exchanged, I'd just rather do it after the heat of summer.
You can wait. The Pool will be a challenge to keep the water sanitary, but that is up to you. The error of a cya test at that level is at least+\- 20%. pH testing will not be valid.
 
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PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
How did you get 200 ? With the dilution test or just what it looked like. If you did the dilution test please list what parts you used and in what order. It still may be off.

It’s irrelevant in a way that it’s so high it pretty much needs be drained, but still. Let’s zero in on it and know for sure. :)

I did a diluted test. I followed these steps-

1. I filled the collection tube (#9191) with 7 ml of tap water and 7 ml of pool water, mixed, then removed 7 ml of the diluted mixture.
2. I added 7 ml of R-0013 to the diluted mixture and mixed that solution for 30 seconds.
3. I went out and, with my back to the sun, slowly added the mixture to the small comparator tube until the black dot disappeared. This occurred at 100, the first line on the register.
4. I multiplied 100 x 2 to get my result - 200.
 
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PoolParadise

Member
Jun 30, 2020
11
Frisco, TX
You can wait. The Pool will be a challenge to keep the water sanitary, but that is up to you. The error of a cya test at that level is at least+\- 20%. pH testing will not be valid.
Thanks Marty. When you say the pH testing will not be valid, do you mean it will not be valid at all due to the high chlorine? I've seen in the Taylor FAQ that high chlorine can make the solution turn purple or blue, but that hasn't happened to me. I haven't seen anywhere that it can invalidate pH testing entirely but I guess I wouldn't be surprised that high concentrations of anything can mess up test results. I am seeing color changes in my results so I know that adding the Borax has done something, lol.
 

mknauss

Mod Squad
TFP Expert
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May 3, 2014
51,245
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Once the FC exceeds 10 ppm, the pH reagent is effected. True, you likely had a pH of 4.5 or lower, and the effect was not as you described.
If you insist on not exchanging this water now, you should get a pH meter. The Apera pH20 will give you accurate pH data at any FC level.
 
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