Chlorine levels rising despite no adjustments in feeder.

[deenamccauley]

I have a bit of a mystery, well to me anyway, I'm sure someone on here can figure it out for me.
We run an automated system for 12% chlorine and for muriatic acid.
I have no problems with this system and have been using it successfully for 4 years now.
My question is why would the chlorine level climb during the day when nothing has been adjusted.
Right now I have the ORP level set at 605 and the feed level at 600. It has been that way for a week at least.
As long as we don't have too many swimmers my test results stay fairly steady but when we have lots of swimmers the chlorine levels climb by the end of the day. That just makes no sense to me.
My test results today:
10 am TC 3.4 2 pm TC 3.2 8 pm TC 7.4
CC .2 CC .2 CC .1
Alk 150 150 150
CYA 25
I hope I have explained this well enough but feel free to ask me any questions. My alkalinity has been running high all season but it has been down to 200 at times but that has been the only thing different this year.
Hope someone can clear this up for me.
Thanks

 

[JasonLion]

ORP readings do not always directly correlate with FC levels. ORP levels can be affected by other things that have nothing to do with sanitation. If something happens that drives the ORP level down, the system will automatically compensate by raising the FC level, which is exactly what you are seeing.

I notice that you didn't write down the PH readings. My first guess would be that the PH is fluctuating because of the bather load, which then affects the ORP reading. However, there is no way of knowing what is really happening without more a lot more information. Even then it isn't always obvious.

When using ORP, it is usually best to just accept that there will be some deviations from the ideal FC level and not worry about it.

 

[deenamccauley]

ORP readings do not always directly correlate with FC levels. ORP levels can be affected by other things that have nothing to do with sanitation. If something happens that drives the ORP level down, the system will automatically compensate by raising the FC level, which is exactly what you are seeing.

I notice that you didn't write down the PH readings. My first guess would be that the PH is fluctuating because of the bather load, which then affects the ORP reading. However, there is no way of knowing what is really happening without more a lot more information. Even then it isn't always obvious.

When using ORP, it is usually best to just accept that there will be some deviations from the ideal FC level and not worry about it.

Thanks Jason
Sorry, thought I put down the PH levels. They were 10am 7.2 2 pm 7.3 8 pm 7.3
I do understand the concept of how the automated system works. It just makes no sense to me that if I am not adjusting the ORP control and it is not feeding chlorine into the pool, why would my chlroine levels jump that much in a day.
The PH is not fluctuating much, I really stay in that 7.2 to 7.2 range most of the time.
I do use MPS when I get a combined chlorine of .2 plus, but that doesn't read at TC just as CC, right?
I was just trying to explain this to the health inspector because he did not understand why I was putting up my chlorine levels so high by the end of the day. I'm telling him I have asjusted nothing and it is not feeding so I really can't explain it.

 

[JasonLion]

Even a small change in the PH is going to result in a noticeable change in the FC level.

MPS can be problematic when used with an ORP controller. MPS will raise the ORP level, which lowers the FC level. MPS will read as CC on the drop tests.

 

[deenamccauley]

Even a small change in the PH is going to result in a noticeable change in the FC level.

MPS can be problematic when used with an ORP controller. MPS will raise the ORP level, which lowers the FC level. MPS will read as CC on the drop tests.

Sorry, I just must not be explaining myself well. I would think that after a day of heavy use, the chlorine levels should drop.....not rise by 4 points. Yesterday it went from around 3 to up to 7 by the end of the day, despite the chlorine feeder, not feeding any chlorine into the pool. The Ph only fluctuated by .2
Thanks for your input

 

[JasonLion]

The FC level can't have gone up if the chlorine feeder was off and you didn't add any chlorine manually. Either, the chlorine feeder was actually on, or your test results are wrong. I have been assuming that the chlorine feeder was actually on.

 

[deenamccauley]

The FC level can't have gone up if the chlorine feeder was off and you didn't add any chlorine manually. Either, the chlorine feeder was actually on, or your test results are wrong. I have been assuming that the chlorine feeder was actually on.

I'm not trying to be difficult Jason. I know what was in the pail at the begining of the day and I know what was in it at the end of the day. And I know what the ORP was set at and if it ran at all it ran very little and there is next to nothing out of the pail. I check it very often.
I don't think I ever said the feeder was off....i said it was not feeding during that time frame, or if it was feeding it was not feeding enough to warrent a 4 point increase.
I use a Taylor test kit and have been using it for years so I'm not sure what I would suddenly be doing wrong. My reagents are fresh. I don't add chlorine manually unless I need to shock.
Thanks anyways....didn't mean to annoy you.

 

[JasonLion]

I'm not annoyed at all. I just think you need to question your assumptions. The required amount of chlorine either got in the pool or your test result is wrong. Neither one is likely, but one of them must have happened.

 

[deenamccauley]

I'm not annoyed at all. I just think you need to question your assumptions. The required amount of chlorine either got in the pool or your test result is wrong. Neither one is likely, but one of them must have happened.

Some thing just occured to me. We had trouble with a back up valve a couple years ago and had pool water coming into the muriatic acid pail. I am going to test the chlorine pail to see if that might be happening with it.
That might explain the full pail.
Is there any other way to check a back up valve....or should I just replace it and see if that changes things.

 

[deenamccauley]

So that was the problem, pool water was siphoning back into the chlorine holding bucket. It was then pumping into the pool but the bucket appears to never get emptyer.
I've replaced the back up valve and so far so good.
I'm thinking that should maybe just be part of my regular maintenance every season. I already replace lines every season but hoped those would last a little longer because they aren't cheap.