Chlorine Loss Rate

[mikesig83]

Hi - I added bleach to my pool last night and checked the reading this morning. FC was showing as 12 and now eleven hours later it is 3.5. Is that normal. I live in the Dallas area.

This was my reading this morning:
FC - 12
CC - 0.0
Ph - 7.8
TA - 120
CH - 240
CYA - 50

That seems like a lot of Chlorine to lose in 11 hours. Thoughts? Thanks

 

[mknauss]

Hard to tell. You get alot of loss due to the sun when well above your target level FC.

Do a Overnight Chlorine Loss Test. Best way to tell if there is an issue.

How does the water look?

 

[GOONiE]

Test chlorine at dusk and then check again at dawn

if you lost more than 1ppm. Time to do a slam. You have organics in your pool.

If your chlorine holds holds up overnight. Your daily FC loss is due to the sun.

 

[Richard320]

Hmm.

Using this chart from Pool Water Chemistry

It looks like the half-life of chlorine is about 6 hours at 50 CYA. So 12 FC would drop to 6 FC in 6 hours and then to about 3 FC in another 6 hours, so it seems you're in the ballpark. But I agree with you: it still seems awful high. You might have something growing in the water. If it lost its sparkle or is looking cloudy you've found your answer. An Overnight Chlorine Loss Test will confirm things.

 

[mikesig83]

Hmm.

Using this chart from Pool Water Chemistry

It looks like the half-life of chlorine is about 6 hours at 50 CYA. So 12 FC would drop to 6 FC in 6 hours and then to about 3 FC in another 6 hours, so it seems you're in the ballpark. But I agree with you: it still seems awful high. You might have something growing in the water. If it lost its sparkle or is looking cloudy you've found your answer. An Overnight Chlorine Loss Test will confirm things.

Thank you all. I’ll check on the loss overnight.

 

[mikesig83]

Water look terrific-FYI. Nice and clear no algae on walls.

 

[mopar440_6]

Water look terrific-FYI. Nice and clear no algae on walls.

Good call on the OCLT. By the time you see the algae its too late. If you do have something starting it'll be a lot easier and shorter SLAM if you start while everything looks good.

That said, I have a similar issue with our pool. No shade at all so on bright sunny days I lose FC in a hurry. I've seen similar losses this time of year with our pool. We're in the middle of a SLAM at the moment but I usually average 1/2-1 gallon a day of 12.5% in maintenance mode with a 40-50 CYA level.

 

[mikesig83]

I lost 1 ppm of FC last night. I guess I'll do a SLAM?

 

[mknauss]

Technically you passed. But a day at SLAM level may not hurt.

Up to you.

 

[mikesig83]

Technically you passed. But a day at SLAM level may not hurt.

Up to you.

Seeing that now. I agree. It can't hurt.