Thoroughly stumped on combined chlorine reading

cvette

In The Industry
Feb 3, 2019
5
Virginia
#1
Hi,

We are having a peculiar issue at our aquatic facility with one of our pools. As of November of this past year we have started seeing combined chlorine levels of no lower than 0.2 PPM. It's not unusual for it to spike up to 0.8 PPM even. In an effort to remedy this issue we have shocked the pool several times in the past month. We have shocked it to break-point for 12 hours, 16 PPM FAC for 18 hours, and even 20 PPM FAC for over 24 hours. The next time the water is tested before the facility is opened we will still find a combined chlorine reading of 0.4 PPM, 0.6 PPM, or even 0.8 PPM still. We do have a Hanovia UV system installed that unfortunately stopped working in early December that will be replaced in the coming weeks. Looking back at our test logs, even when the UV system was operating normally we still had chlorine splits. I have also asked that our staff stop using non-chlorinated shock to rule our potential interference with the FAS-DPD test - this still has not shown improvements.

Our local pool store across the road has tested our water multiple times using the same test kit that we use and has explained to us that there's no CC reading at all. Which is strange as they're using the same kit, and preforming the test identically to how we would. We took a water sample to another pool store out of town that uses a computerized system for testing and they have found there to be a 0.6-0.8 split as expected. Strangely, they informed us that unless our CC level is above 2.0 PPM there's no need to shock. I spoke with several people at the store including service managers, and they all agreed that 2.0 PPM or above is the action level.

Confused, and dumbfounded we re-examined every single thing we do to test the water. Sanitizing our test kits, using brand new reagents, sampling from different locations around the pool, testing our fill water, making sure we are preforming the test exactly the way Taylor has explained. Nothing. Still high combined chlorine. Does anyone have a hunch on what may be the cause of this, and how we could effectively lower our CC?


Here's a little info about the pool in question:

Indoor/Outdoor: Indoor
Capacity: 88,000
Surface: White concrete w/marble dust, and blue quartz aggregate
Sanitizer: Pulsar Plus Cal-Hypo briquettes
Shock: Pulsar Plus Power Shock (79%)
pH control: Co2 feed, and/or muriatic acid
TA control: Soda ash
Turnover Rate: 3.5 hours
Features: Dumping buckets, arch jets, gusher fountain, water slide, zero entry
Occupancy: Typical weekday sees probably 50-100 swimmers, weekend around 100-200
Backwash frequency: Once a week
Filter type: 31 FT sand filter

Typical chemistry:
FAC: 2.0 PPM
CC: 0.6-0.8 PPM
TC: 2.6-2.8 PPM
pH: 7.3-7.5
TA: 100
CH: 300-500
CYA: 0
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
#2
Welcome to the forum! :wave: A couple items to highlight before we go too far in this thread .... one - We emphasize accurate pool owner testing with a TFP-recommended test kit (TF-100 or Taylor K-2006). We give very little credence to any pool store testing. The other item is that you are in the industry and operating what appears to be a commercial pool, so you probably have some local issues to contend with there as well. But I'll start off with some basic TFP items.

Here at TFP, if the CC is at/below 0.5 we consider it the same as zero. Basically non-consequential. In your situation, it may be slightly elevated depending on the time of day, amount of swimmers, and amount of oxidation. The oxidation is critical and a bit unclear for us as we have no way of knowing how much sun the water actually receives to help dissipate those CCs. You might give us more details about that issue. I think you noted this, but of course certain sanitizers contain MPS products which can spike the CC as well.

We also use a FC/CYA Chart to balance those two items for ideal efficiency. Again though, your local industry requirements may vary. Even in a completely indoor pool, we generally recommend a small amoutn of stabilizer to assist with not only the harshness of the chlorine, but in your case even a minimal amount of sunlight which could impact that FC consumption rate.

I'm sure others will tag along on this discussion, so stick around for more info and make sure to read our to learn a bit more about the TFP philosophy. We'll do what we can to help get you some answers. Welcome.
 

mknauss

Mod Squad
May 3, 2014
12,217
Laughlin, NV
#3
Welcome to the forum!

CC's build up in indoor pools and eventually, even with a properly sized UV system, you must drain a significant amount of water to reduce them.
As you use Cal Hypo for chlorination, your calcium builds up and I suppose you have to drain significant amounts of water to reduce it. Does the CC levels correlate with those drain/refills?
 

cvette

In The Industry
Feb 3, 2019
5
Virginia
#4
Welcome to the forum! :wave: A couple items to highlight before we go too far in this thread .... one - We emphasize accurate pool owner testing with a TFP-recommended test kit (TF-100 or Taylor K-2006). We give very little credence to any pool store testing. The other item is that you are in the industry and operating what appears to be a commercial pool, so you probably have some local issues to contend with there as well. But I'll start off with some basic TFP items.

Here at TFP, if the CC is at/below 0.5 we consider it the same as zero. Basically non-consequential. In your situation, it may be slightly elevated depending on the time of day, amount of swimmers, and amount of oxidation. The oxidation is critical and a bit unclear for us as we have no way of knowing how much sun the water actually receives to help dissipate those CCs. You might give us more details about that issue. I think you noted this, but of course certain sanitizers contain MPS products which can spike the CC as well.

We also use a FC/CYA Chart to balance those two items for ideal efficiency. Again though, your local industry requirements may vary. Even in a completely indoor pool, we generally recommend a small amoutn of stabilizer to assist with not only the harshness of the chlorine, but in your case even a minimal amount of sunlight which could impact that FC consumption rate.

I'm sure others will tag along on this discussion, so stick around for more info and make sure to read our to learn a bit more about the TFP philosophy. We'll do what we can to help get you some answers. Welcome.
Thanks for the reply. The Taylor k-2006 would be what we use throughout our pump rooms here at the facility. We have a LaMotte ColorQ but I have unfortunately not found it to be accurate nor consistent. The pool itself does receive a consistent amount of sunlight on ons side of the pool throughout the day. There are rather large 5ft x 3ft glass window panes that run wall-to-wall and an additional 60 ft up to the ceiling. As we are about to change over to Accu-Tab feeders I will keep your suggestion in mind regarding the CYA!

Welcome to the forum!

CC's build up in indoor pools and eventually, even with a properly sized UV system, you must drain a significant amount of water to reduce them.
As you use Cal Hypo for chlorination, your calcium builds up and I suppose you have to drain significant amounts of water to reduce it. Does the CC levels correlate with those drain/refills?
Hi,

Since I have started working here the pools have not been drained completely, or even partially. I asked about this and it seems the last time this pool was drained completely was in August of this past year. The calcium hardness was never an issue according to staff so they never bothered to do partial drains.

Maybe irrelevant, but I'll mention that our other pools have never had a combined chlorine problem. The therapy pool is around 26,000 gal, and the main pool is 1,120,000 gal. They both see about the same amount of swimmers as the pool in question.
 
May 10, 2017
1,753
Hays, Kansas
#6
It's recommend for a commercial outside pool to run about 20 cya for clorine harshness reduction and still excellent kill times and clorine effectiveness. You will have to run more FC normally and also check your local regulations. Do some searches here particularly from 'chemgeek' if you want to know more.

Your high cc problem could be from some hidden algae growth since it seems regular. Have you checked all the nooks and crannies around the pool such as lights and ladders? Have your scubbed the walls and floor with a clear such as a robot or pressure side cleaner?
 

cvette

In The Industry
Feb 3, 2019
5
Virginia
#7
It's recommend for a commercial outside pool to run about 20 cya for clorine harshness reduction and still excellent kill times and clorine effectiveness. You will have to run more FC normally and also check your local regulations. Do some searches here particularly from 'chemgeek' if you want to know more.

Your high cc problem could be from some hidden algae growth since it seems regular. Have you checked all the nooks and crannies around the pool such as lights and ladders? Have your scubbed the walls and floor with a clear such as a robot or pressure side cleaner?
Sorry for the late reply. Yes, we checked all the nooks and crannies for any suspect algae growth. We also vacuum nightly with a robot.

I did want to give you guys an update as of our latest attempt to remedy this situation. Last night I drained our pool down a little over 1' and replaced with fresh water. I haven't seen a change in our CC as of this morning. I imagine we should ideally go a lot lower than that but that's all we had time for unfortunately. I would like to try and schedule a deeper drain at some point soon.
 

Donldson

TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
3,287
NW Ohio
#8
Most municipal water sources use monochloromines to sanitize water since they are less volatile than unstabilized chlorine. That is possibly what you are seeing after a drain and refill.
 

cvette

In The Industry
Feb 3, 2019
5
Virginia
#9
Most municipal water sources use monochloromines to sanitize water since they are less volatile than unstabilized chlorine. That is possibly what you are seeing after a drain and refill.
This was something I was reading about a few weeks ago. I spoke with the director of our WTP and they said that they still use unstabilized chlorine.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,492
Tucson, AZ
#10
Organic CC, those derived from the reactions of chlorine with organic compounds such as creatinine and urea (components of sweat and urine), will not breakdown even past “breakpoint chlorination”. Breakpoint chlorination only deals with inorganic CCs like monochloramine. UV light does not help either once the persistent CCs form.

You have to drain the pool to lower the CC levels. Typical state health codes consider anything above 0.2ppm CC’s as actionable.

If you do continue to use non chlorine shock, then you must get the MPS interference removal reagents from Taylor.
 
Likes: MyAZPool

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,173
Pleasanton, CA
#11
There are rather large 5ft x 3ft glass window panes that run wall-to-wall and an additional 60 ft up to the ceiling.
The glass would likely inhibit the transmission of UV radiation which is necessary to break down the CC. You need direct sun exposure without anything in-between.
 

cvette

In The Industry
Feb 3, 2019
5
Virginia
#13
Would like to see pictures of this pool, looks awesome!
I'll PM you some pictures!

In another update. We did some experiments today leaving one 5 gal bucket of pool water out in the sun for 2 hours resulting in 0 FAC, 0.6 CC.

We left another bucket in the pump room that we've done nothing to. After about 2 hours that bucket is reading 0 FAC, ~0.2 CC.

I would have thought the opposite would have happened...