Very high Cyanuric Acid with no obvious reason

Hello all. I have a vinyl lined pool of 16,000 gallons. I've always had good luck maintaining my balance using the 3-inch chlorine tablets that contain stabilizer.

When returning from being away last summer, I noticed the CYA was very high. So I stopped using the tablets and maintain my water with Clorox diluted and distributed well after sunset.

PoolMath says to replace over 50 % of the water which is not an easy option here in the desert.

I cannot figure out why it is still so high after stopping the tablets last October.

Any thoughts on why it's so high or suggestions on how to lower the CYA?

Thanks for this great forum!
 

Mendy48

Bronze Supporter
Apr 27, 2018
634
Midland, MI
Your one recourse would be to replace 50% of your pool water with fresh water. That is the only way to get your CYA down. How are you testing your CYA? Do you have your own test kit and if you do, what is it.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
5,265
Northern NJ
maintain my water with Clorox ...
Read the label on your Clorox bleach bottles carefully. Here in the USA almost all Clorox bleach says it contains "Cloromax Technology". That is polymers that are not suitable for pools or spas. You need to be using pure bleach or liquid chlorine with no additives of any kind.
 
Welcome to the forum!
CYA does not disappear quickly. It mostly is removed only when you take the water in the pool out and replace with fresh water. And that does NOT include evaporation.

How did you test for the CYA level?
I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.
I use
Mel,

How many bags of "shock" do you throw in your pool each week/month???

Jim R.
Thanks for the questions. I appreciate your taking the time to consider my issues.
I have had this p
ool for 15 years and never had this particular problem.

My pool gets little use. It is located very close to the Pacific Ocean. Until last October, I have been able to maintain my chemicals using PoolMath suggestions. Primarily used 3-inch trichlor tablets, muriatic acid and algaecide. I used to have to raise my CYA using the powder in a sock method. But now it is very high.
I have used In The Swim Lithium Shock occasionally, maybe once every 4 weeks but always after a good rain and at the first sign of algae. Two one-pound bags in my 16,000 gallons. I am ready to order more lithium shock but see it has been discontinued.
I use Aquacheck7 test strips, purchased recently, expiring December 2020, kept in a cool dark place.
Right now I'm having trouble keeping my TC and FC up. I shocked April 18, but keep getting very low chlorine readings. I've added one gallon Clorox April 21 and April 23. Still very low, TC at 1, FC at .5. Although using Blue Devil OTO test drops I do show 1.0 Chlorine reading.
Here are my latest readings using the AquaCheck 7 strips:
Total hardness: 1000
Total Chlorine: 1
Free Chlorine: .5
PH: 8
TA: 240
CYA: 200

I have added 3 liters of muriatic acid slowly over the past 10 days.

I replace evaporated water (about 1/4 inch a day) with well water from our private neighborhood well.

I buy my Clorox at Costco in Cabo San Lucas and don't find the word "Cloromax" anywhere on the label.

I know replacing water is the suggested way to get CLA down, but water here in the desert is in short supply and extremely expensive, if you can even get a large quantity at one time. Plus I've been told not to empty a vinyl liner pool as the liner is probably brittle now. I replaced the liner after Hurricane Odile in 2014. I'm hoping there is another way to get in balance.

Thank you all for any help with this!
 

justinc

Gold Supporter
Apr 3, 2019
141
Texas
Unfortunately the test strips aren't accurate. You'll need to get a test kit like the Taylor 2006-C in order to know how your water chemistry is doing. I personally have tried using test strips and the readings are totally erratic and not something I would trust before adding chemicals. Maybe to check if everything is in order before a quick dip, but not for routine monitoring and maintenance. They just aren't accurate enough.
 

Mendy48

Bronze Supporter
Apr 27, 2018
634
Midland, MI
Agree with Justin

Also, when you see the first sign of Algae, it means that you FC is below the target level. You have to maintain Free Chlorine in your pool at all times; meaning you should never let you Free Chlorine to fall below the target level. Use liquid chlorine or regular bleach (the plain stuff - no splashless, scents, or polymers. No Clorox or cloromax - no additives) to maintain your Free Chlorine level. However, you're going to need a more reliable test kit to begin with. Get your test kit (TF-100 or Taylor K-2006C). We recommend the TF100 from TFTestKits.net or the Taylor K-2006C. Once you get your test kit, please post your results here (FC, CYA, pH, TA, CH, CC).

All you need to maintain your pool is Chlorine or Bleach & CYA (stabilizer). Muriatic Acid and Borax to manage PH on a periodic basis as needed. But lets first start you off in the right track. Get your test kit so you can accurately measure and balance your pool accordingly.
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
15,296
Laughlin, NV
Shock is not a process. It is a one time thing or product. SLAM is a process.

You need a kit to measure FC greater than 10 ppm to properly SLAM. Strips are as good as guessing.
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
15,296
Laughlin, NV
Is there another way to measure CYA other than the strips?
Strips are no better than guessing.
 
I actually do have a Taylor FAS-DPD Chlorine test kit that yesterday afternoon shows my FC to be 3.4. I have no confidence in the strips now. I regret purchasing 4 new bottles last month from Amazon.

I'll be ordering the test kit you recommend but getting it here in Mexico takes at least 2 weeks. Checking with the local pool store to see if they might have it and also liquid chlorine without additives.

Thank you for helping me understand more of how this works.
 
Strips are no better than guessing.
Thank you! I will order this!
 
I've ordered the TF100 kit and the CYA test kit, It will take at least 2 weeks to receive.
In the meantime,I am planning to drain 15-18 inches from my pool, using the "drain" setting on my Jacuzzi sand filter valve, and replace the water right away.
Am I risking (1) my vinyl liner, which is 4 years old, or (2) damaging or losing sand from my filter by pumping to "drain" for an extended period?
Thank you!
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
15,296
Laughlin, NV
You are better off to use a sump pump. Can you buy one in your location? Could you put where this pool is located in Mexico in your profile?

As long as you do not drain more than 18" or so your liner should be OK. There is an exchange method but you need a sump pump.
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
15,296
Laughlin, NV
Allen - draining a small amount now is not going to hurt anything - and it is very likely the CYA is too high based on past use of trichlor.
 

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