Loosing chlorine - running out of ideas...

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gatorbrit

gatorbrit

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LifeTime Supporter
Aug 22, 2013
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Raleigh,NC
I've been loosing chlorine for most of June! I am running an intellichlor ic 40. Pool is 3 years old, swg is in its second year.

CYA 60-65
PH 7.5
Salt 3200
All other numbers are good and pool is sparkly clear.


Here's what I've done

Based on prior suggestions:

1. 6/14: Slammed pool to TC = 30. (8 bottles of bleach).
TC fell steadily after that even with the SWG running 100% for 12 hours/day


2. performed an OCLT on 6/19.
Night reading: TC=9, FC = 8.5
Morning reading (about 9am) TC = 8.5, FC =8.0

So I lost 0.5, but I was a bit slow getting the morning reading.

Last night 6:30pm TC =8.5, FC =8
Just now 6:30 pm TC =6.5, FC=6

So today I lost TC =2, but the SWG was running all day at 100%. It had run for 11 hours at the time of the test.


A couple of other bits of info:
The SWG is one year old. I cleaned it with muratic acid at the start of the season.
It's been very hot and sunny here in NC - high 90s. We've also had a lot of rain - but none last night.
Last year I was able to hold chlorine running the pump for 6-8 hours at 80%.

I am stumped as to what's going on - seems unlikely that the SWG is broken and how would I check anyway? Do an OCLT with the swg running?

Any suggestions?
 
As shown in this post, the Pentair Intellichlor IC40 outputs 1.40 pounds of chlorine in 24 hours. If you type in the following in a Google search:

1.40 pounds per 24 hours per 18000 gallons in milligrams per liter per hour
Click to expand...

you get the following:

0.388326385 (milligrams per liter) per hour
Click to expand...

So your IC40 should output around 0.4 ppm FC per hour. That should be more than enough to handle normal chlorine loss. Since you don't have any significant overnight chlorine loss with the SWG turned off, it appears the loss is due to sunlight during the day. However, at your CYA level that loss shouldn't be very high, probably not more than 3 ppm FC, and your IC40 should be able to handle that easily.

So yes, why don't you do an OCLT with the SWG running and see what you get since you already know the chlorine loss rate is low. If you run for 12 hours, you should get around 12*0.4 - 0.5 = 4.3 ppm FC gain overnight. If you get significantly less, then there is something wrong with your IC40 not producing enough chlorine. Check for calcium carbonate scale on the plates. Check to make sure your salt level is high enough.
 
chem geek said:
As shown in this post, the Pentair Intellichlor IC40 outputs 1.40 pounds of chlorine in 24 hours. If you type in the following in a Google search:



you get the following:



So your IC40 should output around 0.4 ppm FC per hour. That should be more than enough to handle normal chlorine loss. Since you don't have any significant overnight chlorine loss with the SWG turned off, it appears the loss is due to sunlight during the day. However, at your CYA level that loss shouldn't be very high, probably not more than 3 ppm FC, and your IC40 should be able to handle that easily.

So yes, why don't you do an OCLT with the SWG running and see what you get since you already know the chlorine loss rate is low. If you run for 12 hours, you should get around 12*0.4 - 0.5 = 4.3 ppm FC gain overnight. If you get significantly less, then there is something wrong with your IC40 not producing enough chlorine. Check for calcium carbonate scale on the plates. Check to make sure your salt level is high enough.
Click to expand...



Wow - thank you! Great explanation. OK - it's almost dark here so I'll do another test and then set it running through the night.
 
Ok, that covers the chlorine generation. To pursue the organic consumption side of your chlorine loss. Did you remove your light and clean out the niche, if you have one. And have you done a deep clean on your sand filter recently? We've seen lots of algae in both. Here's how to Deep Cleaning a Sand Filter
 
pooldv said:
Ok, that covers the chlorine generation. To pursue the organic consumption side of your chlorine loss. Did you remove your light and clean out the niche, if you have one. And have you done a deep clean on your sand filter recently? We've seen lots of algae in both. Here's how to Deep Cleaning a Sand Filter
Click to expand...

I'm running the system tonight to see how much we generate over night. Will report the numbers tomorrow. Hopefully, deep cleaning the sand filter isn't needed - it looks like a lot of work!!
 
OK results to report.

last night 10pm: TC=7.5, FC=7.5
this morning 7:30 am: TC=10, FC=10

Pump ran non stop for 9.5 hours. I gained 2.5 ppm CL.

This is less than the 0.4*9.5 hrs = 3.8 which is what Chem Geek predicted.

So either:

--- Something is still eating CL (although my OCLT doesn't indicate this - so unlikely) - but if the filter is the source of the organics, then the OCLT wouldn't have found this because the pump was off.
--- Maybe I don't have enough salt. The salt light is good and on 6/13 I tested and showed salt was 3200.

Today I will add more salt, and then repeat the test overnight again.
 
The level of salt The level of salt doesn't change the output of chlorine. It is either good or not.

There are 3 choices I can think of
Organic matter using chlorine
Cell is not generating as much chlorine due to age/dirty
Pool volume is bigger than the calculation

Every time I see your user name I see gatorbait. LOL I guess from living in New Orleans for a while.
 

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Ok. I will run an OCLT tonight with the pump on but the swg off. That should give me a more accurate read on whether there are organically somewhere in the system.

I am surprised that salt level doesn't matter. Does this mean that below some level, chlorine production just stops, but above that level it is good?
 
pooldv said:
The level of salt The level of salt doesn't change the output of chlorine. It is either good or not.

There are 3 choices I can think of
Organic matter using chlorine
Cell is not generating as much chlorine due to age/dirty
Pool volume is bigger than the calculation

Every time I see your user name I see gatorbait. LOL I guess from living in New Orleans for a while.
Click to expand...

Just wanted to follow up on this - I am pretty sure that the pool size is about right. Last year the SWG would do a great job at about 60% for 8 hours a day. So something is different this year.

As for gatorbrit - I am a UF grad and a british ex pat. Hopefully not gatorbait!

cheers
 
The salt level would matter if the power supply were constant voltage since a lower salt level would have lower conductivity, lower current, and lower chloride ion concentration. If the power supply is outputting constant current, then the lower salt effect on conductivity won't matter since the power supply voltage would be higher, but a lower chloride level WILL produce less chlorine and more oxygen gas which is why one must have higher chloride levels in the pool for an SWG in the first place. It's not just for conductivity. Nevertheless, this effect isn't that large for the kind of lower salt level you might have.

Imagine an extreme example where one used potassium sulfate salt instead of sodium chloride salt. There would be NO chlorine generated because there would be no chloride to convert to chlorine. So of course the chlorine output is dependent on the chloride salt concentration, even if the voltage is raised to keep the current the same. If there isn't as much chloride to make chlorine, then more oxygen gas will be made instead.
 
New results:

First to recap - I posted this earlier.

6/21/15: OCLT with pump on and SWG on.
10pm FC = 7.5
7:30am FC = 10.

Gain of 2.5, less than the 3.8 predicted.

6/22/2015
Pump and SWG 100% ran all day.
7:30am FC = 10.
7:30pm FC = 8.5.
Loss of 1.5, despite running 12 hours, 100%
Very sunny and hot (close to 100F)

So that evening I did:
OCLT: with pump on but SWG off. (to see if there is algae)
8:30pm FC=8.5
7:30am FC = 8.5

The pool passed the OCLT with no loss.



Bottom line is that I am concerned that this is a problem with my 1 year old IC 40. That it is just not outputting enough CL. I cleaned it last night (inspected it and acid washed it) and it looks good - no build up, so I am pretty concerned as I can't think of anything else that it could be.

I also checked the CYA and it is about 60-65. I could push it up a bit I guess, but I am surprised that this would be the cause of so much day time loss.

I appreciate any suggestions.
 
hmmm, not sure about the IC40, but the recommended CYA for SWG is 70 to 80 .... it may have alot to do with not holding the FC that the IC40 is creating... Can't remember, where you able to get it checked at the store, maybe it is going bad?? Is it under warranty?
 
Update:
I removed and cleaned the IC 40 - acid wash and hose pipe. I also upped the CYA a bit.

Latest results from running the OCLT last night with the pump on and the swag running is that I gained 3.5 CL. This suggests to me that perhaps there was some debris in the SWG that was inhibiting CL production. The numbers are still not quite where I think that they should be but they are better. I'll keep an eye on it.


For future reference, here are the steps I took in dealing with the issue.

1. Check all levels are good - salt, ph, cya etc.
2. run an OCLT with the pump on, SWG OFF to determine if there is an algae issue (in my case there wasn't).
3. run an OCLT with the pump on, SWG ON to determine the output of the SWG (in my case: initially this seemed low).
4. do a thorough clean of SWG per manufacturers instructions.


One final question though: I know CL loss is related to sunlight, but is it also a function of the temperature of the water? My pool is pretty warm right now - around 90F - could that increase CL loss?

Thanks

Rich
 

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