Chlorine too high

[lsaad]

Hi all,

My daughter had a serious facial surgery this summer and hasn't been able to swim all summer. She is finally all healed and got the ok to swim yesterday, but now our chlorine level is too high. Argh. She was so looking forward to swimming so I feel terrible! I'm new to pool maintenance so I'd love your input on how to quickly fix this and get my daughter swimming as soon as possible! Many thanks in advance

Here are our stats:

In ground pool, 20,000 gallons, DE filter system, using "Taylor Complete FAS-DPD chlorine" test kit system to test

Current numbers:

FC = 7.5 (down from 8 yesterday after running filter all night, getting rid of some water and adding fresh -- maybe a few inches worth)
CC = .5
PH = 7.2 (up from 7.0 yesterday after adding soda ash)
TA = 40
CH = 120
CYA = Out of CYA regent so could not take this number, will go to store to get more

 

[duraleigh]

Swim away. That FC is fine if you have ANY CYA at all. Even if you have zero it is still OK.

 

[Donldson]

Welcome to TFP!

I'm willing to bet you are working off the old numbers that say 1-3 is good? That has been around forever, since long before CYA was studied and it's effects on chlorine was established. This chart shows the proper free chlorine levels based on CYA level. It is completely safe to swim in any level up to the shock level on that chart. Unless you have literally no CYA whatsoever in your pool (very, very unlikely) your FC is completely safe to swim in. So don't let her miss another minute due to outdated numbers!

You could stand to bring your pH and TA up a touch though. Judging by that do you use tablets to chlorinate? If so then definitely get a CYA reading soon. It's important to keep an eye on that when you use tablets.

 

[lsaad]

Hi! Thank you both so much for your quick response -- you have made my daughter's day We are heating up the pool now and jumping in this afternoon -- she is thrilled!!

And thank you for the updated info about FC. Yes, I was using the old info -- I had no idea that was wrong.

Regarding the CYA, I just tested it with a test strip just to get some kind of idea. I know that's not terribly accurate, but it shows about 75. If that's about right, then I should be aiming for an FC of 8 and no lower than 5, according to the Chlorine/CYA chart, correct? This is much different than what I have been doing. I had been aiming for about 1-4 FC, so I'd like to be sure I've got this right.

Also, yes, I do use tablets. Could you say more about what I should be keeping an eye for CYA with the tablets? And how does using tablets affect the pH and TA and what should I be aiming for there?

I can't thank you enough again for your help! You lifted the whole mood in our house -- it has been a long summer for my daughter. She is so happy today though!

 

[Donldson]

Very glad to give some good news, hope she enjoys getting back in the water!

If a pool had zero CYA then 1-4 FC would be correct, but then the sun would burn it all off in an hour. CYA helps protect chlorine from the sun but also has a buffering effect, the more there is the more FC is kept buffered, so more FC is needed to be effective. So we tend to keep CYA in the 30-50 range, which gives a good balance between sun protection and buffering. Too low and you lose a lot to sunlight. Too high and you need to maintain very high levels of chlorine, which is safe (because most of it is buffered) but difficult to do.

Tablets are made from trichlor, which is chlorine stabilized by CYA. As they dissolve they release chlorine as well as CYA, so your level is always rising. Trichlor is also very acidic (which is why it has such a strong smell) and so as it dissolves it lowers your pH and TA. While the pH and TA are easily fixed with soda ash, the CYA can only be removed by replacing water. As you learned today you should be keeping about 8 FC, but as your CYA rises you will need to raise your FC level to compensate. This is why most of us do not use tablets. If you like them then it is a good idea to drain and replace some water weekly to keep the CYA from building up too high.

There is a lot of information in the Pool School that can teach you more about different chlorination methods and the pros and cons of each, but for now I think getting your daughter in the pool is the most important thing! Have a great afternoon in your pool, and we are here to answer any more questions and help you with anything you may need!