Clear Water but Still Failing OCLT During SLAM

wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
I started my SLAM 3 days ago after I failed an OCLT and the water was a bit cloudy.

The water was crystal clear the next day, I’ve brushed & vacuumed daily and I’ve maintained my FC levels as recommended for a SLAM (16 with a CYA of 40). CYA was in the 70-80 range but I replaced about 1/3 of my water prior to SLAMing.

Is it “normal” to have what appears to be very clear water, combined with a CC level of zero and still continue to fail a OCLT for a couple days during a SLAM? I think I’m doing everything right...so stay the course and be patient?

I have read stories of SLAMs lasting over a week, but I started out fairly clean - I think. Just couldn’t maintain my FC levels while running my SWG at 60% for 12 hours daily, with a CYA of 80.

Thanks
Bill
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,132
NW Ohio
Keep at it, the only way to lose chlorine overnight is that something is still in the water. Make sure you check every nook and cranny, light fixtures, ladders, corners, any place algae might be hiding and biding its time for a comeback.

If the water looks good then don't be afraid to use the pool during the day. SLAM FC levels are still fairly comfortable to swim in, especially compared to a non-TFPC pool. I think a lot of people get especially discouraged by prolonged SLAMs because they don't use their pools during it. Going for a swim is safe during the process and as long as you test and dose shortly after use it won't prolong things further.
 

Oly

Gold Supporter
Jun 28, 2017
2,317
Fresno, CA
Pool Size
27000
3 ppm FC loss overnight is significant. Stay the course and reread Donldson's post above, key on the first two sentences. Take your time when testing and add full uniform drops of reagent.
 

wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
3 ppm FC loss overnight is significant. Stay the course and reread Donldson's post above, key on the first two sentences. Take your time when testing and add full uniform drops of reagent.
I try to control the drops, but my R-0871 consistently and immediately drops three drops as soon as I turn the bottle over without any squeezing. It then settles down and I can slow it down and control it. I figure as long as it’s a consistent process I should be able to compare results with confidence. I’m using a very new TF-Pro kit.

Thanks for the help.
 

Mdragger88

Bronze Supporter
Jun 1, 2018
2,980
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Definitely check your crannies! Like @Donldson mentioned- algae likes to hide. Weir doors, light niches, ladder cups, water features etc.
 

wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
What’s frustrating is the pool is only 6 months old with very few crannies...just 4 steps, 3 lights and 4 returns. Plus my overnight FC losses really haven’t declined significantly from night to night. I’ll brush everything real good as suggested and stay the course.
 
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Mdragger88

Bronze Supporter
Jun 1, 2018
2,980
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Perhaps also re check your cya level to be sure you’re at the proper fc slam level. FC/CYA Chart
Also try testing a few (30 min) after dosing to be certain you’re reaching the targeted fc level. You may have older bleach or underestimated pool volume.
 
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wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
I'm new to this and I could use some advice, before the wife gives up on me managing our pool! I'm hearing it's "time to call in the professionals".

I'm on day 6 of a SLAM. The water was never very bad looking, just slightly cloudy and the pool itself is only 6 months old, so everything is quite new. After day 1 of SLAM water already looked crystal clear to me and certainly now at day 6, where I can tell I'm missing a small screw on my main drain cover in deep end. My CC has also tested zero since day 1. My problem is I can't pass an OCLT. Every night I lose around 2.5 - 3.0 in FC.

Is there something else going on, other than a water problem? Some of my thoughts...
  • Maybe my last bleach add is not mixed well enough before testing for the OCLT, even though I run my VSP at 100% for an hour before nightly testing. Otherwise I've been running my pump at 60% 24/7 during the SLAM.
  • Is my heater, which is sitting dormant during the SLAM a possible culprit for any contamination?
  • I brush daily, but is it critical to also vacuum (I have to do this manually)? I'm not getting any "dust" anymore while brushing.
  • I've retested my CYA level since starting the SLAM and I still in the 30-40 range. Does it hurt to increase my target FC from 16 for a while? I've already increased the recommended bleach by 25% to account for possible old bleach and this certainly gets me over 16.
1623150571470.png
Thanks in advance for any advice!
Bill
 

Texas Splash

Mod Squad
TFP Expert
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Jun 22, 2014
33,434
Texas, San Antonio/Marion, South-Central Area
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Bill, it certainly appears you've been vigilant. But something is amiss for such a large overnight loss. We need to rack that code because I guarantee the pool store will not. So let's go over some other items:
- Your 3 lights, are they the small LED type? No hollow niche behind them like a standard large halogen light?
- Are you grabbing your water sample from the same location and depth?
- How old is your FAS-DPD?
- Have you considered removing the drain cover to inspect underneath the lid and inside that drain area?
- The heater if off but water running through it correct? If so, that's fine.
- Cell has been off and you're just using liquid chlorine correct?
 

wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
- Your 3 lights, are they the small LED type? No hollow niche behind them like a standard large halogen light?
YES, small LED type

- Are you grabbing your water sample from the same location and depth?
YES, away from returns in deep end, at least elbow depth
- How old is your FAS-DPD?
New TF-Pro kit received last month
- Have you considered removing the drain cover to inspect underneath the lid and inside that drain area?
Have not done this
- The heater if off but water running through it correct? If so, that's fine.
Heater is off, and connected -- not sure if water runs through it when off however
- Cell has been off and you're just using liquid chlorine correct?
Yes, cell has been off and using liquid chlorine exclusively

On the idea of inspecting under my drain cover, what might I find or be able to see here? I guess my imagination could run wild and assume a small animal got in there during construction 6-7 months ago...must be something significant, don't you think, rather than a few leaves, etc.?

Thanks for the help!
Bill
 

Texas Splash

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Jun 22, 2014
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Texas, San Antonio/Marion, South-Central Area
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On the idea of inspecting under my drain cover, what might I find or be able to see here?
In a pool that seems to be lagging on the OCLT, we know there must be something somewhere. It sounds as though you have eliminated all of the typical areas we would have concerns with. While the drain seems unlikely with such a new pool, it's about the only area that hasn't been inspected. We have seem owners remove the lid to find algae, so unless there are hollow steps or a ladder in the water, that would seem to be the last place to check.
 
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Mdragger88

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Jun 1, 2018
2,980
Hernando, Ms
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Intex Krystal Clear
Does it hurt to increase my target FC from 16 for a while?
We always round up on the cya test so anywhere between 30 & 40 is considered 40ppm. 16 is the SLAM level.
 

mknauss

Mod Squad
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May 3, 2014
44,003
Laughlin, NV
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Just to cover all the bases, clean the vial you are using for the FC test. Use bleach. Rinse well.
 
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wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
Just to cover all the bases, clean the vial you are using for the FC test. Use bleach. Rinse well.
The best part of cleaning the vial is the reduced surface tension inside, meaning it much easier to fill it precisely with the proper volume of pool water. No meniscus to speak of.

Running another OCLT tonight - really didn’t do anything different except I avoiding adding bleach a few hours before testing (more time than other nights) and I shut off water to my auto-fill, just to ensure no fresh water is introduced if instance I have a leak somewhere - never know with a new pool.

Still hoping I don’t have to remove my main drain cover which has about 8 screws to it.
 

Katodude

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Aug 22, 2017
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Your other option is get a hose nozzle that puts out of good stream of water. Get down there and blast the drain with the hose see if you can agitate the stuff that is underneath the drain. Then fill a container that you can cover the opening with your thumb with LC (like a spray bottle container). Then go down there and dump the LC right in the drain. No guarantees but those things might be enough to kill anything that is living under the drain cover. But still easier than removing it.
 

wjmano

Gold Supporter
May 19, 2021
53
Wildwood, FL
I passed my OCLT last night! My FC was only down 1.0, versus my usual 2.5-3.0.

A big "Thank You" for everyone's help!

I'll now let my FC drift downward and add CYA to get it up from the current 40 ppm. Will also plan to take a closer look at my main drain and try Kato's idea, just in case that was part of my problem -- sounds like fun.

And will likely run another OCLT tonight...although I hate the possibility of failing it.
 

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