High CYA: Whats the worst that can happen?

[Yeeper]

My understanding of CYA is that the correct amount protects your chlorine, too little will put the chlorine at risk of being burned up quicker. And too high means the chlorine will not be effective...correct?

So why does the pool store acknowledge CYE but don't seem concerned about a high level? Their ALEX program calculated it at 143 and they said it was all good, no big deal to have it that high. ...ummm...OK.

I'm not going to go into my local store and say "but TFP says this, and TFP says that." I just don't operate that way. But I'd still like to know why.

Lets say I never found TFP and didn't do a water change, but kept adding liquid chlorine for the summer. At greater risk of algae? Poor sanitization etc.?

Quite possibly overthinking this as my gut tells me the right answer. Guess I'm just looking for reassurance. Sorry and thanks.

 

[mknauss]

Lets say I never found TFP and didn't do a water change, but kept adding liquid chlorine for the summer. At greater risk of algae? Poor sanitization etc.?

Yes. To maintain active chlorine levels sufficient to kill person to person disease and algae you would need to maintain a FC over 8 with a CYA of 140.

Take care.

 

[kabutotx]

Correct.
As long as you keep your FC to above 10% of your CYA, you should be fine. I had 140 CYA when I moved in and kept it fine till I could drain for that and high CH.

 

[Demegrad9]

You are correct, if you never found TFP and just kept adding liquid chlorine all summer you'd be at a greater risk of algae and more likely poor sanitation.

But you did find TFP and technically if you just add enough liquid chlorine to maintain a high enough FC, you will mitigate those risks. I did this last year where I had ~120ppm CYA at the beginning of the summer from previous home owners so I just maintained 14ppm FC then. As the summer went along, I just kept checking CYA and adjusted my target FC level as appropriate. Pool was beautiful all summer. Now after partially draining during closing and all the rain water, I've finally got CYA under control at about 40ppm.

 

[JoyfulNoise]

There are two functions to cyanuric acid in pool water. The first is that it acts as a stabilizer to cut down on UV loss. Without cyanuric acid, the chlorine half-life would be about 28mins or so. With cyanuric acid, the half-life will increase to almost 8 hours. The second function of cyanuric acid is to act as a chlorine buffer, that is, the CYA holds the oxidizing chlorine atom in reserve (by bonding with it) and thus lowering the overall concentration of hypochlorous/hypochlorite in solution. This buffering reduces the harshness of chlorine and also slows down the formation of the more irritating chloramines and other disinfection by-products.

If one solely focuses on the UV screening effect of cyanuric acid, then yes, more is better. This is where pool stores tend to be. If you look at cyanuric acid holistically and understand the equilibrium chemistry, then you come to the conclusion that too much CYA can lead to too low of a drop in active chlorine levels and thus increases the likelihood of algae and disease transmission. This is why TFP developed the FC/CYA dosing chart - it avoids the pitfalls of using too much CYA.

 

[Yeeper]

Yes. To maintain active chlorine levels sufficient to kill person to person disease and algae you would need to maintain a FC over 8 with a CYA of 140.

Take care.

Yep. All of the replies make sense. So this is how the stores operate, as Joyful Noise mentioned.

Thanks everyone!

- - - Updated - - -

Correct.
As long as you keep your FC to above 10% of your CYA, you should be fine. I had 140 CYA when I moved in and kept it fine till I could drain for that and high CH.

Yea I was considering this but I don't think we'll get to use the pool much for another few weeks so I'll probably just suck it up and do the drain. But thanks for offering the tip. Makes me feel better than it "can" be done.

 

[skimmerswimmer]

So why does the pool store acknowledge CYE but don't seem concerned about a high level? Their ALEX program calculated it at 143 and they said it was all good, no big deal to have it that high. ...ummm...OK.

Because they can make lots and lots of money by telling you to keep your FC between 1-4 ppm which is way too low for a CYA of 143 creating a perfect environment for algae to grow.

Then they tell you "Here...you need shock, and some algaecide, and some clarifier, and some magic potions! It's only $1000, but you will have somewhat clear water for a few days. If it doesn't work, we will sell you lots of other stuff to combat that pesky pool of yours!"

 

[Teald024]

Their (pool store) ALEX program calculated it at 143 and they said it was all good, no big deal to have it that high. ...ummm...OK.

I'm not sure who this ALEX fella is or how he measures the CYA, but if it is a melamine test, then it is only accurate to ~100ppm. If a level is measured above 100ppm, then a diluted test should be performed. See the Extended Test Directions post#8 for how to do this. You could very easily have CYA well above 140ppm.

We really recommend that you invest in your own test kit such as the TF-100 or Taylor K-2006C. I personally like the TF-100 better because I feel the amount of reagents in that kit are better suited for the home owner.