Unable to maintain Mustard level SLAM during the Daytime

shoyru177177

Member
Sep 24, 2021
5
Long Island, NY
Hello everybody! I'm here for some advice in lieu of my buddy who has been shocking his pool first to 20ppm FC and then later having bumped it to a target minimum of 30ppm FC due to a recent algae bloom that may be mustard algae. He's in Central Florida and has a 1718 gallon above-ground vinyl pool that he brought down to a pH of about 7.2 before starting the SLAM. Him and I have consulted together trying to follow TFP ideas on SLAM and it's been about 3-4 days that he's been in this process and he is using liquid chlorine.

Pool Stats:
1718 Gallons Above-ground Vinyl Pool
50ppm CYA
pH lowered to 7.2 before start of SLAM
10.5% Liquid Chlorine
0ppm CC every test
330GPH Cartridge Pump

We are both quite confused as to how he is supposed to maintain SLAM levels when he goes out to work in the daytime from the times of 3pm-12am. The pool's FC levels drop significantly due to the sun, sometimes more than 10-15 FC during the day when he is not around to add liquid chlorine. Are these significant dips harming the mustard SLAM process? I read around that at his CYA levels of 50ppm he should be maintaining an FC of at least 30 for multiple days (and/or?) until he has no FC loss to ensure having killed off mustard algae.

It took at least two nights of blatant FC loss, but on the third night, he got two readings about an hour-and-forty minutes apart from one another that both returned as 32ppm FC in the pool. His target FC for those two measurements was 33ppm at the time. He ended up running out of FC test reagents and unfortunately couldn't continue testing that night for any more data. The following night since then had shown varying amounts of FC loss in the tests that were done approximately 3 hours apart from one another. One test returned about 6.5-8ppm FC loss and the next one returned 1ppm FC loss.

His pool had started out increasingly cloudy with greenish/brown dust on the bottom that poofed into a cloud if you disturbed it. He had taken care to vacuum the pool with his garden hose-powered vacuum on low pressure with additional socks within the mesh bag to catch as much of the algae dust as possible, and then on a following day, brushing around the floor of the pool to stir up dust that was settling in places. The pool has gotten significantly clearer each day even though it seems some algae dust might still be present around the seams in the floor. He has a 330gph cartridge filter pump that has been running 24/7 from the start of SLAM and rinsed out approximately every day during the SLAM process. At least one of those times the filter was entirely yellow-green. It seems things are definitely improving, but we are confused in how he can end this ordeal because he is tired of the repeated nightly testing and the bleach fumes. To us it seems clear that he needs to keep going to hopefully eradicate this potential mustard algae because it would be a waste of effort if he stopped sooner than he should and then it decides to grow back in a week or two.



I wanted to know if anyone could please shed some light on these points:

1. Why might his FC loss be fluctuating all over the place when some times it seems like it's practically done and then it hits like a truck the next time?

This next question below is the one I'm most concerned about:
2. How is he supposed to maintain 30ppm FC during the day when he's out of the house and the sun eats anywhere from 10ppm FC and up? (One reading on the second day said 18.5ppm FC was lost from 5:00am to 2:30pm!)


Thanks for reading and thank you to anyone who decides to offer any ideas!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,347
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
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shoyru177177

Member
Sep 24, 2021
5
Long Island, NY
Welcome to the forum!
Remember that one must pass the normal SLAM Process prior to raising the FC to Mustard Algae SLAM FC level for just 24 hours. Read Mustard Algae - Trouble Free Pool
But with that volume pool, far more economical to dump the water and start over.
I suggest you read ABC's of Pool Water Chemistry.
Thank you for your speedy reply!

I had a few questions around what you suggested.

1. Do you think he has so much SLAM FC loss in the sun because of the small capacity of the pool, compared to a pool with like 30,000 gallons at the same CYA level? Would this not happen if he fully passed the SLAM criteria at 20ppm before moving up to 30+ ppm?

His original goal on the first night was to shock to 20ppm but after 4-5 tests that night, the pool was still losing varying amounts of FC. At least one or two of the test readings sent us for a loop, because in one reading the FC came back at least 3ppm higher than what he had put in the pool, and it confused the both of us, and that made it so we weren't sure what to think about the following reading to try to gauge FC loss. Starting that night after the last test around 5:00am we agreed to bump the FC to 30ppm in hopes that it would stay above 20ppm until the time he woke up that afternoon. It ended up dropping to 12ppm FC by 2:30pm. Since then his target FC had been 30ppm for each bleach addition.

2. If he were to continue trying to SLAM, how is he supposed to make it through the sunlight hours without having the pool drop to like 12 FC? The SLAM Process page quotes in regard to SLAMming "You cannot do this overnight…it often takes several days to see it completed…no shortcuts." I am struggling to find any information on how to continue carrying out a SLAM during the daytime when the sun is destroying everything. Considering his pool is significantly visibly clearer now, is it worth salvaging and continuing the SLAM? Or should he just drain anyway?

3. If he were to drain, is there a recommended concentration of bleach to scrub the pool with, and for how long to make sure the algae is dead before refilling? Can the algae reinfect the pool from the same garden hose that was used to drain it being used to refill it with water? How would one go about sanitizing the pump and all of its tubing and cartridge to avoid re-contamination? Am I simply overestimating the algae's ability to repopulate once it's foothold has decreased significantly?


Thank you so much! Here are some pictures from when he first noticed something afoot on the 9/12 and when he started to attempt SLAM on 9/20. We had thought it was pollen for nearly a week until it slowly and then suddenly got a lot worse. The pool has been clearer and clearer by the day since the start of SLAM.
pool shock.png
 
Last edited:

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,347
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Water depth can effect FC loss. Very shallow will lose it quicker as there is not as much UV protection.

When you follow the SLAM Process, you test and add chlorine to get back to SLAM level FC as often as you can. As long as the FC is above minimum for the CYA, it is killing algae.

Drain, clean with diluted bleach (say 10 parts water to 1 part bleach), and refill. Anything in the lines will be dealt with by the FC level after filling.
 
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shoyru177177

Member
Sep 24, 2021
5
Long Island, NY
Water depth can effect FC loss. Very shallow will lose it quicker as there is not as much UV protection.

When you follow the SLAM Process, you test and add chlorine to get back to SLAM level FC as often as you can. As long as the FC is above minimum for the CYA, it is killing algae.

Drain, clean with diluted bleach (say 10 parts water to 1 part bleach), and refill. Anything in the lines will be dealt with by the FC level after filling.
Thank you! I will refer my friend here to see your suggestions! I'll be back if there's anything to update. Thanks again.
 

shoyru177177

Member
Sep 24, 2021
5
Long Island, NY
My friend decided to stay the course and continue the SLAM because he's already over a week into it at this point, and the pool has been so clear. He reduced his nightly SLAMS to target 20ppm FC in accordance with the SLAM instructions. In the hours from dawn to 2pm it burns off to usually sit at 10-12ppm and then at 2pm he bumps it back to 20 before heading to work. It burns back off to around 12-15ppm again in the hours after, until he gets home past midnight and can bump it back to 20ppm FC. He is passing OCLT with a loss of 0-0.5ppm FC and always returns a reading of 0ppm CC (skeptical that maybe his brand new CC reagent is faulty?).

I wanted to know-- in the SLAM passing criteria, it says something along the lines of having "clear water." His water is crystal clear and yet some days there's a gunk line collected in the seams at the bottom that he either sweeps towards the filter intake or he vacuums up with his mesh and socks. When he sweeps it towards the filter, the filter picks up a decent amount of it, but I suppose the rest of it gets dispersed in the water from the sweeping and then re-settles by the next day. When he vacuums it with the mesh bag and the socks, he is able to collect more of it and it takes longer to come back. Is having this gunk preventing him from passing SLAM under the criteria of "clear water"? Because the SLAM article isn't specific enough.

Water depth can effect FC loss. Very shallow will lose it quicker as there is not as much UV protection.

When you follow the SLAM Process, you test and add chlorine to get back to SLAM level FC as often as you can. As long as the FC is above minimum for the CYA, it is killing algae.

Also, when it comes time to mustard SLAM at target 30ppm FC for 24 hours, am I understanding it correctly from your SLAM explanation that he just bumps up to 30ppm whenever he can over the duration of 24 hours? Or is the mustard SLAM criteria more strict of never falling below 30ppm FC?


These following two photos are from 9/25, three days before the time of writing.
obujsx58.pngn8d4t4p6.png

This next photo is his dirty filter from today, 9/28.
d2v4d7nz.png
 
Last edited:

ferretbone

In The Industry
May 24, 2016
161
tx
That does not look like yellow algue in your last pictures. If that does not brush of it's not algue, it's a stain. Bush that off, it looks like dead green algue or a stain.
 

shoyru177177

Member
Sep 24, 2021
5
Long Island, NY
That does not look like yellow algue in your last pictures. If that does not brush of it's not algue, it's a stain. Bush that off, it looks like dead green algue or a stain.
It doesn't leave a stain. It gets vacuumed or brushed and then it comes back in a day or two depending which method was used. I know he more often just brushes it towards the filter because he doesn't have time before he goes to work.

Does this stuff being present mean the pool doesn't pass SLAM finishing criteria? ("Clear water") Do I move on to the mustard SLAM part of the process?


pool5.pngpool52.pngpool53.png
 
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