Still Failing OCLT

[Awp14]

I have been failing the OCLT for over two weeks now, usually by 2 FC. I’ve read a lot of threads on here over the last week of people dealing with the same issue but I am not making much progress.

My pool water is very clear and was before I started, but the FC had dropped to 0 while we were out of town so I decided to start the SLAM process.

I am 95% sure my CYA read 60 before I started so I had been maintaining FC at 24 but after the first week, I started maintaining FC at 28 in case my CYA reading was off and it’s actually 70. I’ve been brushing, adding chlorine at least 3-4 times per day, vacuumed here and there. The water is still clear and there is no debris in the pool, but when I brush I am still seeing very slight/small brownish clouds in some cases. It hasn’t seemed to improve so I am unsure if it’s pollen or what.. pool is in full sun the entire day.

Here are a couple OCLT readings I have written down:
5/23 - Day 10 - 22 FC to 20 FC
5/29 - Day 16 - 26 FC at 11pm to 24 FC at 5:30 am

Are there any suggestions besides brushing every single spot in the pool, vacuuming, maintaining levels and continuing on? I’m not sure vacuuming is helping with the small brown clouds I am seeing but I’ll keep going unless I hear otherwise. Should we clean the filter? We just replaced the cartridges a month or so ago and I’m wondering if they are not working as expected. Filter is Pentair 420 clean and clear 160301.

Anyway, thanks so much for any help, I am tempted to give up since this has always been a quick and easy process for us in the past.

 

[Texas Splash]

I would clean the cartridges if it's been a while. Also make note of the filter gauge to ensure it's working (going to zero when off) to ensure it didn't go back over the winter. Interesting you keep failing with exactly 2 ppm.

Any chance your FC math is incorrect? Are you using the 10 ML water sample size with one scoop of powder, mixing until clear and dividing the result in half? For example, it would take 48 drops to clear to equal an FC of 24?

 

[Texas Splash]

I forgot to ask, to confirm, has the pump been on 24/7 to keep the water mixed well for a good water testing sample?

 

[Awp14]

I would clean the cartridges if it's been a while. Also make note of the filter gauge to ensure it's working (going to zero when off) to ensure it didn't go back over the winter. Interesting you keep failing with exactly 2 ppm.

Any chance your FC math is incorrect? Are you using the 10 ML water sample size with one scoop of powder, mixing until clear and dividing the result in half? For example, it would take 48 drops to clear to equal an FC of 24?

Yes, it’s driving us a little crazy that we keep failing at 2 PPM. One night ago it was 1 PPM but I had forgotten and tested at 2 AM and 6:30 AM, which I realize is not a full night!

Yes, that’s correct for the number of drops and FC math - making sure to keep drops uniform and swirling while adding.

Cartridges were brand new a month ago but we will clean them today.

 

[Awp14]

I forgot to ask, to confirm, has the pump been on 24/7 to keep the water mixed well for a good water testing sample?

Yes the pump has been on 24/7 unless off for 15 minutes at a time to let water settle before vacuuming.

Thanks so much for responding.

 

[Texas Splash]

Well shoot, I was hoping perhaps we might discover something relatively easy to help you out. Then with those things ruled out, and assuming your reagents are relatively fresh, we have to go back to SLAM basics to ensure something isn't still growing in there. So a quick recap of things if they apply to your pool:

- Cleaned behind the skimmer weir door?
- Pool cover (if applicable) pulled back/cleaned?
- Light niche (if applicable) exposed and cleaned?
- Main drain cover inspected/cleaned?
- Pool ladder/handrail removed/cleaned?

Of course there's the all-enjoyable CYA test itself. You mentioned taking it up to 70 to be safe which makes sense. Hopefully it's not actually higher.

I made an assumption earlier but should probably confirm .... your SWG has been off during this entire time correct?

 

[Awp14]

Well shoot, I was hoping perhaps we might discover something relatively easy to help you out. Then with those things ruled out, and assuming your reagents are relatively fresh, we have to go back to SLAM basics to ensure something isn't still growing in there. So a quick recap of things if they apply to your pool:

- Cleaned behind the skimmer weir door?
- Pool cover (if applicable) pulled back/cleaned?
- Light niche (if applicable) exposed and cleaned?
- Main drain cover inspected/cleaned?
- Pool ladder/handrail removed/cleaned?

Of course there's the all-enjoyable CYA test itself. You mentioned taking it up to 70 to be safe which makes sense. Hopefully it's not actually higher.

I made an assumption earlier but should probably confirm .... your SWG has been off during this entire time correct?

Yes SWG has been off the whole time. I have new reagents arriving this week but the ones I’m using should be ok I think?

Things that apply, I apologize as I am not too familiar on a couple of these:
Light niche - do I need to take the light out of the side of the pool and clean it? Do I need to drain the pool to do this? We have one small LED in the pool and one in the spa.
Main drain cover - are these the drains in the bottom of the deep end? Or part of the pool equipment that is above ground?

I will clean the skimmer doors, I had brushed in the skimmer area but not specifically the doors! Thank you!

 

[Texas Splash]

Main drain cover - are these the drains in the bottom of the deep end?

Yes, in the bottom/deep end.

Light niche - do I need to take the light out of the side of the pool and clean it? Do I need to drain the pool to do this? We have one small LED in the pool and one in the spa.

If all of your lights are LED, then probably no need to remove. The larger halogen lights are mounted into a hollow niche that can get stagnant over time. LED are not the same. So only if you have a large halogen type bulb with a niche should you remove the light. Those lights can be removed because the niche is filled with water anyway.

 

[Awp14]

Yes, in the bottom/deep end.


If all of your lights are LED, then probably no need to remove. The larger halogen lights are mounted into a hollow niche that can get stagnant over time. LED are not the same. So only if you have a large halogen type bulb with a niche should you remove the light. Those lights can be removed because the niche is filled with water anyway.

Ohh ok. I will try to find some documentation on here on how to clean those drains. Thank you so much for the suggestion! And sounds like we will just scrub around the lights for now and not remove them. Thank you again!

 

[Texas Splash]

I don't think we discussed this earlier, but if your pool is relatively new, the drain covers may not be a big deal. Some owners of older pools have removed the drain covers to find a mess under there. So it's completely your call. For safety reasons, be sure the pump is NOT pulling water from the main drain(s) should you attempt to remove the cover.

 

[Bperry]

Also note if the CYA measurement is wrong and you are overdosing the chlorine, that may be the issue as well. FC that’s higher than SLAM level burns off much faster.

 

[Awp14]

I don't think we discussed this earlier, but if your pool is relatively new, the drain covers may not be a big deal. Some owners of older pools have removed the drain covers to find a mess under there. So it's completely your call. For safety reasons, be sure the pump is NOT pulling water from the main drain(s) should you attempt to remove the cover.

Ok gotcha! The pool was put in spring of 2019.

 

[Awp14]

Also note is the CYA measurement is wrong and you are overdosing the chlorine, that may be the issue as well. FC that’s higher than SLAM level burns off much faster.

Ok thanks so much, that helps. Just to clarify, does it matter what the FC is at night for the OCLT, should it be exactly at SLAM level, or is the test purely about the loss calculation? I have been making sure it’s near the correct level at night (between 22-28) and just calculating the loss.

 

[Texas Splash]

does it matter what the FC is at night for the OCLT, should it be exactly at SLAM level, or is the test purely about the loss calculation?

During a SLAM, we typically maintain the FC for the OCLT because we don't want the pool owner to lose progress, but the OCLT can be accomplished at any time with just about any FC level. So if soon you find no improvement with that odd 2 ppm loss and everything else is otherwise perfect, you might consider allowing the FC to fall down to about 10-15 ppm. FC testing can get a little tricky with the higher FC levels.

 

[Awp14]

During a SLAM, we typically maintain the FC for the OCLT because we don't want the pool owner to lose progress, but the OCLT can be accomplished at any time with just about any FC level. So if soon you find no improvement with that odd 2 ppm loss and everything else is otherwise perfect, you might consider allowing the FC to fall down to about 10-15 ppm. FC testing can get a little tricky with the higher FC levels.

Ok thank you very much, I will keep this in mind!

 

[Awp14]

In case anyone else references this in the future, we FINALLY passed the overnight chlorine loss test today on day 18. We had vacuumed and cleaned the filters on Monday but didn’t pass Tuesday morning - still off by 2 PPM. So yesterday we let the FC drift down to 12 as suggested and it was still 12 this morning before sunrise. Wish I had tried that sooner as I’m thinking we probably would have passed a week ago, but THANK YOU again to Texas Splash for the wonderful suggestion!