What's wrong with a high CYA?

CapCrown

New member
Jan 31, 2020
2
Jacksonville, FL
I'm a new pool owner of about 3 months in NE FL. I have a roughly 13k pool/spa with blue speckled marcite and a screen enclosure. I've done the test kit and I always have greater than 100 CYA and I've been keeping my stats as follows : FC 8, CC 0, TA 100, PH 8.0 (I struggle to keep PH low) and my pool looks great. It's crystal clear and doesn't really smell like chlorine. I also have a decent amount of salt still in my pool as the last owners removed the SWG and switched to chlorine. Is it bad to be using the pool with these numbers for the next month or so? I'm trying to grow a lawn and its taking a lot of water so i dont want to water my lawn and fill a pool for a few more weeks. After the lawn is good to go I do plan on draining half and refilling though.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,334
Northern NJ
Welcome to TFP.

How much greater then 100 is your CYA?

Do you have your own Test kit like a TF-100 or K-2006C?

The higher the CYA then the higher you need to keep your FC to prevent algae growth. In general you need a FC about 12% of CYA. So accurately knowing your CYA is important to set your FC target.

And with a FC over 10 your pH test is not valid.

How do you chlorinate your pool?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,334
Northern NJ
Is your pool test water above 70F for the CYA test?

Do step 8 in the CYA test...


  1. If your CYA level is 90 or higher, repeat the test adjusting the procedure as follows:
    1. Fill the mixing bottle to the lower mark with pool water.
    2. Continue filling the mixing bottle to the upper mark with tap water.
    3. Shake briefly to mix.
    4. Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark.
    5. Continue the test normally from step 2, but multiply the final result by two.
 

CapCrown

New member
Jan 31, 2020
2
Jacksonville, FL
Is your pool test water above 70F for the CYA test?

Do step 8 in the CYA test...


  1. If your CYA level is 90 or higher, repeat the test adjusting the procedure as follows:
    1. Fill the mixing bottle to the lower mark with pool water.
    2. Continue filling the mixing bottle to the upper mark with tap water.
    3. Shake briefly to mix.
    4. Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark.
    5. Continue the test normally from step 2, but multiply the final result by two.
My pool temp is around 80 F and my CYA seems to be right at 100 mark. I've just been using the calcuator with a FC target of 8 and I test every few days and add to put it back at 8. I also have the TF-100 kit.
 

ping

TFP Expert
LifeTime Supporter
Jun 24, 2011
3,134
Long Beach, CA
Welcome to TFP!

You should do fine for a little while like this but you're asking for trouble soon.

Drop the pH a bit and keep the FC above 8 and you will be fine. Like Allen said the pH test is not accurate when the FC is above 10 so make sure when you test the pH that the FC is no more than 10.

To prevent the pH from rising fast you will want to lower the TA which will slow down the pH rise. Keep reading in Pool School and you will learn many things like this.
 
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Leebo

Admin
TFP Expert
LifeTime Supporter
Jul 21, 2011
10,070
Eastern Ohio
Two issues with keeping a 100ppm CYA level,

First, the test maxes out once you hit 100ppm. Yes you can dilute it to get a ballpark idea, but you’re reducing the accuracy of the test. If you’re at 100 and are using pucks, you’ll have an issue. If you’re at 100 and use a SWG, you have a chance as you won’t be adding even more CYA.

Second is the increased level of chlorine needed to clear up green. As the temps increase you’ll be gambling more and more with this. If you get any algae, you’re in a load of trouble and will be draining.
 
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JJ_Tex

Bronze Supporter
Jul 17, 2019
1,723
Prosper, TX (DFW)
Also keep in mind that unless you are just adding liquid chlorine, you are adding CYA as well every time you add pucks, shock, etc. Pretty soon your 100 CYA turns into 150 CYA and your FC of 8.0 will be tied up by the CYA and not be able to fight algae.
 
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Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
1,620
Rancho Cucamonga, CA
All the the comments regarding the disadvantages of running a high CYA are valid. However, if you're vigilant and understand the downsides, you can keep your pool clean. When I came to TFP, my CYA was well over 100 and I was able to maintain a clean and balanced pool for over a year.
I've just been using the calcuator with a FC target of 8 and I test every few days and add to put it back at 8.
Testing every few days is risky when your barely maintaining minimum FC levels. You're FC target is 11-13. Never allow your FC to drop below 8 ppm. Stay on top of FC levels and you'll be fine.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,040
Franklin, NC
I've just been using the calcuator with a FC target of 8 and I test every few days and add to put it back at 8.
How did you pick a target of 8? That is the absolute minimum FC you should ever have. Your target is 11-13.

I understand your pain. I took over my pool with a CYA of about 250 (CYA tests above 100 are just a guess, not very specific contrary to what the pool store says). With a CYA of 250 I had to keep my chlorine level at around 20 just to keep algae away. Yes, it's safe to swim at elevated FC levels as teh CYA buffers the chlorine.

Your pool should never see any solid chlorine products. Liquid chlorine only.

Go down to Home Depot or Lowes and pickup a small submersible pump. Pump water out of the pool toe water the lawn.

If yo don't plan on replacing the SWCG, you need to replace more than half of the water as you really want to be in the 30-40 range.
 

setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
3,483
Stuart/FL
Cap,

Consider re-starting the swg. There are lots of experts here to help if you need it. You'll need higher CYA level and may get by with less water exchange or none. Plus you'll have all the extra time to care for the lawn since swg is sooooo easy!

Chris