Failing Overnight Chlorine Loss Test

[AW139]

Hi All,

This is my first post here, since discovering TFP earlier this year. We recently installed an in ground 10,000 gallon FG pool, and have been doing my best to maintain it the TFP way… now. For the first about month, I didn’t know about TFP so it was maintained it to a lower 1-3 ppm of FC. I have been using the Taylor K2006 for testing. These are my recent levels from this morning at 6am:

FC - 5.5
CC - Detectable, but under 0.5
pH - 7.6
TA - 100
CH - 250
CYA - 50

The problem is that last night I performed the OCLT. At 9 pm last night, my FC was 8.5. I know for a time last week my FC levels would have dropped below my recommend 4-8 ppm levels, since I was away and not as much liquid chlorine was added. I don’t know by how much, or for how long. Liquid chlorine was added daily, but probably not enough.

Everything is else seems normal. Water is totally clear, with no signs of algae growth. Zero organic material visible on the walls and floor when I brush/vacuum. ph slowly creeps up, and I lower it via muriatic acid occasionally.

I suspect a (hopefully short) SLAM is in order to stop the chlorine loss and “reset” back to square one, but I wanted to get some input before I proceeded.

Thanks!!!

 

[ajw22]

Welcome to TFP.

A 3ppm loss overnight indicates algae in the water.

Follow the SLAM Process step by step with no shortcuts.

Get a SWG if you are often away from your pool.

 

[AW139]

Thanks!

SWG is on the budget for next year. I should have just installed it with the pool, but I was uneducated on the topic at the time.


Any advice on when during the SLAM I
should do another OCLT, since the pool already passes the first two tests (clear water and CC below 0.5)? I guess since I’m testing and maintaining at SLAM levels, I should be able to see that the FC isn’t going down much at night and do a proper OCLT at that point?

I’m trying to time doing the SLAM between times I’m away from home for work, since I’m often gone for week or so at a time. I don’t want to start it and not be able to finish it. Should I expect this to take a couple days, or am I looking at longer? I’m hoping since the pool is crystal clear already, oxidizing the invisible algae/organics is a shorter process, but I don’t want to half-Rear the process by having to leave before it’s complete.

 

[ajw22]

You will see when the pool stops taking more chlorine then usual in a day.

You should raise your FC to SLAM level now and stop the algae growth. There is no reason to put it off.

How long it takes depends how often you test and return your FC to 20.

 

[ajw22]

Who adds Liquid Chlorine to your pool when you are away?

 

[AW139]

My wife or step-daughter. They just aren’t comfortable doing the whole SLAM procedure.

 

[AW139]

You will see when the pool stops taking more chlorine then usual in a day.

You should raise your FC to SLAM level now and stop the algae growth. There is no reason to put it off.

How long it takes depends how often you test and return your FC to 20.

Is there any point in raising to SLAM level now, if I’m not going to be able to maintain SLAM levels when I leave in a few days? I’m looking to complete the process correctly, and don’t want to waste chlorine and swim time by failing half way through.

 

[kimkats]

You can and SHOULD do it now! If you wait it will only get worst and take longer in the long run. I am hoping you will only have to SLAM for a couple/few days. They don't even have to do anything else other than add chlorine a few times a day. You can pour the amount you want them to pour into small, closed containers.

 

[wireform]

It also would benefit from a good brushing once a day at minimum.

 

[AW139]

You can and SHOULD do it now! If you wait it will only get worst and take longer in the long run. I am hoping you will only have to SLAM for a couple/few days. They don't even have to do anything else other than add chlorine a few times a day. You can pour the amount you want them to pour into small, closed containers.

Noted! I am worried about the lack of adjustments to the amount of chlorine that will be added each day, but regardless I’m going to start the SLAM process as soon as feasible. I appreciate the help.

 

[AW139]

It also would benefit from a good brushing once a day at minimum.

 

[AW139]

So quick update. Stared the SLAM yesterday at 3pm, by brining the pool up to 21 FC (was aiming for 20). Here is the timeline:

Aug 11, 2:44 pm - 7.0 FC

3:00 pm - Added 4000 ml (13.0 ppm) chlorine

3:20 pm - 21.0 FC

5:00 pm - 20.0 FC

7:00 pm - 19.5 FC

7:10 pm - Added 150 ml (0.5 ppm) chlorine

9:00 pm - 20.0 FC

11:00 pm - 18.0 FC

11:10 pm - Added 600 ml (2 ppm) chlorine

11:30 pm - 22.0 FC … this part confuses me because it went up by 4.0, but was expecting only 2.0 rise

Aug 12, 6:00 am - 20.0 FC

11:00 am - 16.5 FC

11:10 am - Added 900 ml (3 ppm) chlorine

11:30 am - 21.0 FC


CC has been the same the entire time, detectable but 1 drop easily clears it, so under 0.5 ppm CC. Brushed the pool. Nothing to vacuum, but gave it a once over anyways. Hopefully tonight’s OCLT is a success.

One question I did have is do higher levels of chlorine deplete faster? I lost 2.0 ppm last night starting out at 22.0 FC. If I had started out at 8 ppm, would I still expect a 2.0 ppm drop, or would it be more a percentage of the total chlorine that is lost? Because if it’s a percentage, then the pool will likely pass the OCLT at 8 FC.

 

[kimkats]

If you are doing a proper Overnight Chlorine Lost Test you should have no more than a .5 loss. You did the test just right-doing the first test of the day before the sun was on the pool. With 2 lose you did not pass the OCLT There is something eating your chlorine still.

 

[AW139]

If you are doing a proper Overnight Chlorine Lost Test you should have no more than a .5 loss. You did the test just right-doing the first test of the day before the sun was on the pool. With 2 lose you did not pass the OCLT There is something eating your chlorine still.

Good to know, thanks!

I'm still running at SLAM levels, and on the upside my last test showed zero CC for the first time, so that's a plus. I'm hoping for a better outcome on tonight's OCLT as a result.

 

[AW139]

Was just reading over the FAS-DPD Chlorine Test article, and it states that there is a 10% margin of error when using a large number of drops during the FAS/DPD test. This may explain my slightly high FC level of 22.0 when I expected 20.0. Unfortunately this may also mean that the OCLT at 20 ppm might be hard to rely on, since my results are within 10% of my starting number. Am I interpreting this correctly?

 

[ajw22]

Was just reading over the FAS-DPD Chlorine Test article, and it states that there is a 10% margin of error when using a large number of drops during the FAS/DPD test. This may explain my slightly high FC level of 22.0 when I expected 20.0. Unfortunately this may also mean that the OCLT at 20 ppm might be hard to rely on, since my results are within 10% of my starting number. Am I interpreting this correctly?

Yes.

OCLT is best done at a FC of 10 or less.

 

[AW139]

Yes.

OCLT is best done at a FC of 10 or less.

Makes sense. At this point I may let me numbers drift down below SLAM levels in order to get an accurate OCLT. My daytime levels are about what I would expect from UV burnoff, and the chlorine demand is a fraction of what it was before the SLAM. Even after the initial chlorination to bring up to SLAM levels, I have only needed a total additional 1.8 litres to keep it there.

 

[AW139]

Last night OCLT passed.

0.5 FC lost, 0.0 CC. SLAM complete. Thanks everyone for your help!