Combined Chlorine > 0.5

[SwimminPat]

We are having a challenge keeping the Free Chlorine = Total Chlorine.

We have a 1-year old 28,000 gallon Gunite pool. Our pool stays very clear, and we closely the TC, FC, Ph, Total Alkalinity, CYA, and Hardness. Our pool gets a lot of full Sun, has very little in the way of debris, and light swimming loads (couple of adults for a few hours in the day). We have kept the chlorine level on the high side of normal because of the amount of sunlight. We run our filter about 10 hours a day, from 8a-6p. We use a robotic Dolphin cleaner and have a pool service that cleans the skimmers, scrubs the pool, and backwashes the sand filter weekly. We live in the South-Central US, so daytime temps in Aug were Mid 90s, Sept Upper 80s / low 90s, and currently in low 80s (60s at night).

We used a Triclor tab auto-chlorinator until the CYA got too high (80) this summer, then drained some water and started using liquid chlorine. Our CYA has been in the upper 30s to mid 40s since then. After the CYA got down to 32 we started using the Triclor tabs again to bring the CYA back up towards 50. I test myself using a Taylor K-2006 test kit, but also use our local pool store to compare. Their tests seem to be fairly accurate, but It is the pool store tests that show the TC-FC splits; I don't always see the split with my Taylor Kit, but I don't want to discount the validity of the pool store test. We cannot figure out why the TC / FC split keeps happening.

Today is the fourth occurrence in the past 2 months of CC of 0.5 or greaterer (TC>FC by at least 0.5). We have SLAMed the pool with liquid chlorine using the Pool Math and recently used a granular shock (still trying to get CYA up a bit) with the goal of bringing the TC back equal to the FC.

Current readings:
TC: 10.1
FC: 9.5
CYA: 36
TA: 108
Ph: 7.8
Hardness: 264

Anyone have any idea what could be causing the TC / FC splits?

 

[Msch99]

A: ignore pool store tests, trust your own.
B: If you seldom see .5 cc, you generally don’t have an issue. Maybe poor circulation, maybe a hidden spot on ladder/ skimmer etc. that have a spot waiting to bloom. Maybe swimmer load?
I would check things over, then maybe even raise to slam level a couple days if cc from your tests show up a few days in a row.

 

[Jimrahbe]

Pat,

I would not worry about your CC being more than .5 ppm, unless it continues for several days... or tests...

Thanks,

Jim R.

 

[JamesW]

I don't always see the split with my Taylor Kit

Then it probably does not exist.

I don't want to discount the validity of the pool store test.

Feel free to discount the validity of their tests.

 

[SwimminPat]

Thank you all for the responses. We'll keep testing and see what we see.

 

[JoyfulNoise]

In order to test at the pool store you have to bring a sample in a container. Is the container autoclaved, triple-rinsed and dried with filtered and heated air in between tests? Is it made of an inert material that does not react with chlorine? How long does the water sample sit in your car prior to getting it to the pool store?

Obviously I’m being a bit cheeky with the autoclave cleaning procedure between each use but I’m using sarcasm to illustrate a larger point - the moment you pull a water sample out of the pool it starts to change. If you pull a sample and test it within a few minutes, it’s a reasonably close approximation to the pool water. If you pull a sample, put it a container and then let that container sit in your car while you order lunch at the McDonald’s drive through, it’s going to change. You also have no control over how careful the pool store clerk is being with his own test equipment, how fresh his reagents are or if he just sneezed on your sample prior to testing. That being the case, your kitchen table tests are way more accurate and reliable than a pool store.

 

[SwimminPat]

In order to test at the pool store you have to bring a sample in a container. Is the container autoclaved, triple-rinsed and dried with filtered and heated air in between tests? Is it made of an inert material that does not react with chlorine? How long does the water sample sit in your car prior to getting it to the pool store?

Obviously I’m being a bit cheeky with the autoclave cleaning procedure between each use but I’m using sarcasm to illustrate a larger point - the moment you pull a water sample out of the pool it starts to change. If you pull a sample and test it within a few minutes, it’s a reasonably close approximation to the pool water. If you pull a sample, put it a container and then let that container sit in your car while you order lunch at the McDonald’s drive through, it’s going to change. You also have no control over how careful the pool store clerk is being with his own test equipment, how fresh his reagents are or if he just sneezed on your sample prior to testing. That being the case, your kitchen table tests are way more accurate and reliable than a pool store.

Thanks JoyfulNoise. I appreciate the feedback.