Having trouble passing OCLT

Jump to latest Follow Reply
E

esailer

Member
Jun 22, 2020
8
Arizona - Gilbert
Hi! First off it’s great to be here. Following the methods here has made my pool sparkle.

I just moved into this house on June 14th and it seemed as if the previous owner stopped pool care well before they moved out. Had some algae growing in the water. Was testing at pool store until my brother told me about tfp. Bought a test kit and started balancing my pool.

I’ve cleaned up the algae and the pool is looking incredible the numbers are all looking pretty good but I still can’t pass an OCLT. Last night I tested FC at 16.5 and added liquid chlorine to bring it back up to 18 for SLAM. This morning it had dropped all the way to 4. I added more chlorine this morning to go back up to 18.

I cleaned the filter half a week ago (second time since taking ownership) and it was pretty nasty. I just cleaned the filter again yesterday and it wasn’t as bad but still quite dirty.

do I just keep slamming an eventually it’ll clear up? Are my filter cartridges ok? Do they need to be replaced? The water has looked perfect for a week now and the only issue has been failing OCLT and what I would describe as too much chlorine loss.

current numbers
FC 4 (I did add 2.5 gallons of 10% so this is actually higher)
CC 0.5 (this has stayed 0.5 for the last week)
PH 7.5
TA 160
CYA 45

7FAD6A65-AE42-4B94-8F33-799F137DFC1B.jpeg6E760FED-CE82-4B5A-8A92-01BAA78791E2.jpegD6A58671-1D93-44AD-B55A-1EDCC9721991.jpeg
 
Welcome to TFP! :wave: An FC drop from about 18 to 4 overnight seems very odd indeed. Let's make sure you are doing the FC test correctly. Using the R-0870 and R-0871 (powder & drops), you get a 10 ML water sample, add one generous scoop of powder and mix until clear. Take the number of drops to clear and divide in half. Example: 40 drops equals an FC of 20. Is that how you've been doing it?
 
Texas Splash said:
Welcome to TFP! :wave: An FC drop from about 18 to 4 overnight seems very odd indeed. Let's make sure you are doing the FC test correctly. Using the R-0870 and R-0871 (powder & drops), you get a 10 ML water sample, add one generous scoop of powder and mix until clear. Take the number of drops to clear and divide in half. Example: 40 drops equals an FC of 20. Is that how you've been doing it?
Click to expand...
I've been taking a 10 ML water sample, add two scoops of the powder (turns the water pink) then add drops until clear and divide in half.
 
Okay, the math is correct. One generous scoop is enough for the test.

So now why the large drop? If the FC dropped that much overnight, I'm assuming ti must also drop fast during the day right? The water seems to look good, but something must be off. Have you been following the SLAM Process page correctly? Do you have any hiding places for algae not discovered? Key places are behind the light (niche), under a drain cover, or hollow steps/lagers that are submerged. If any of those apply to you, I would start there. Hopefully you have been brushing daily and cleaning the filter consistently when the pressure increases by 25%. But let us know if you have had any difficulties with the SLAM Process page. We'll try to help you crack the code on this overnight FC loss mystery.
 
Texas Splash said:
Okay, the math is correct. One generous scoop is enough for the test.

So now why the large drop? If the FC dropped that much overnight, I'm assuming ti must also drop fast during the day right? The water seems to look good, but something must be off. Have you been following the SLAM Process page correctly? Do you have any hiding places for algae not discovered? Key places are behind the light (niche), under a drain cover, or hollow steps/lagers that are submerged. If any of those apply to you, I would start there. Hopefully you have been brushing daily and cleaning the filter consistently when the pressure increases by 25%. But let us know if you have had any difficulties with the SLAM Process page. We'll try to help you crack the code on this overnight FC loss mystery.
Click to expand...
there is high loss during the day as well. there is a light, how do I clean behind that? there are two drain covers, how do I clean those? I've brushed and scrubbed the rest of the pool and run the vacuum daily. It seemed like the chlorine loss was slowing but last nights loss has be scratching my head.
 
If you have a standard large light, there should be one screw, probably at the top of the retaining ring, that can be removed to get the light out. Make sure to turn the power breaker off to the light when you remove it and set it on the decking for a couple days while you brush and let the chlorine get in the niche. For the drain covers, there should also be a few screws holding it down. Once you remove the screws, the cover(s) should be removed so you can clean in the drain cavity area and under the grill. Those areas are notorious for hiding algae, and I suspect with this pool's unknown history there may be a bunch in those areas.
 
figured it wouldn't take too long to pull the light out and that I could do it without getting in the pool, I went ahead and popped it out. a bunch of debris came out and the light itself was full of water. going to replace the light. the niche had a nice green/brown dust. I think we found the culprit. still going to do the drain covers this evening when I'm done working, but I'm feeling a lot better now!
 
  • Like
Reactions: Texas Splash
Don't be too discouraged if you fail an OCLT again if you do it immediately. The niche certainly needed cleaning but it typically is not ALL the reason for that large of chlorine drop.

The takeaway is to continue the SLAM. Sunlight and algae (organics) consume chlorine, nothing else, I think you have a ways to go.

Do another OCLT in 24-48 hours from now and meanwhile, brush, vacuum and keep your FC at shock value.
 
I dont know if it would make a difference, but your FC level at 50 cya is actually 20. I dont know if doing it at 18 makes any difference, Im sure someone here would know.
 

Enjoying this content?

Support TFP with a donation.

Give Support
FC level at 50 cya is actually 20. I dont know if doing it at 18 makes any difference,
Click to expand...
I assume you are talking about OCLT value. In theory, it makes no difference where the beginning OCLT FC level is.......you are only concerned about the overnight loss.

While there exists some debate, OCLT starting level could be anywhere from 5-6 ppm or so and go all the way up to SLAM value.
 
@duraleigh From her first post she was using 18 for her FC target for her slam. It should actually be 20. I didnt know if that little bit of difference would matter in her slam success or not.
 
@duraleigh From her first post she was using 18 for her FC target for her slam. It should actually be 20. I didnt know if that little bit of difference would matter in her slam success or not.
Click to expand...
I understand now and I agree with you.......it is a good idea in ANY SLAM to use all the SLAM power that TFP suggests. Probably not a huge difference, but you still want to use as much as possible and that would be 20 ppm.
 
  • Like
Reactions: carnivalday
Changed the pool light today and now have a working light. Cleaned the niche, cleaned under the drain covers and finally found some algae in the little holes where you can attach a safety rope. That little bit was super stuck and took some serious elbow grease to remove but it’s clean now.

was surprised to see FC still at 5.5 eight hours after the last test this morning. Boosted back up to SLAM level and excited to see what I come in at tomorrow.

here’s the old light. I’m guessing the green on the seal probably isn’t a good thing ;)
EC25DD95-B1F3-475A-8F4E-838C252F0680.jpeg4133A5AC-74EB-42D6-8712-259D13117802.jpeg
 
I just want to make sure you are doing OCLT correctly. You are testing in the morning before sunup, correct? If you wait until it is light out, that could bump chlorine loss, although i wouldn’t think at the level you are seeing.
 
It doesn’t get dark here until well after 8pm. You might want to check a bit later.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply