SLAM Mustard Algae?

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poolguy2022

Member
May 19, 2022
11
USA
Pool Size
20000
Surface
Vinyl
Chlorine
Liquid Chlorine
Backstory: Had a brand new pool with algae in it. We could waste out everything at the bottom of the pool and within a half hour, we would have more sand/algae right back on the bottom. It drove it us nuts for the entire summer.

Now: This spring (2022) I find TFP, and we run through a series of tests to determine that we feel it is in fact algae. Our CYA was insane (160+) so we drained the pool and got that down to 50. We cleaned out our filter, made sure nothing was broken and replaced the sand, (note we did this before starting the SLAM though - maybe a week earlier). We are now in the SLAM process. So far, I think its working very well! Each day we have had less and less of the what we believe to be dead algae on the bottom of the pool. We have been doing it for a week today. FC has been at or around/above 20, CC has been fairly consistently 0 with only a couple of days at 0.5. I haven't checked anything else as I've read that the rest of the tests are invalid right now.

Today is the second day in a row where we have passed the overnight free chlorine loss test (OFCLT). There is an extremely minimal amount of the dead algae/sand looking stuff in a few cracks in the pool. So little that it was hard to see at times but it is there. We are thinking/wondering if it is mustard algae and, if so, if would make sense to move into the mustard shock level now that we are 99.5% complete with the regular SLAM (CC was 0.5 or 0 all days), but we have had an extremely minimal amount of dead algae in the morning yesterday and today. Note that it has been a lighter and lighter amount of dead algae each day and the past 3 or 4 days we have had this minimal amount. We have been vacuuming and brushing everything, every nook and cranny each day. One picture is the day it was filled, the other picture is today with a faint line of what we believe is dead algae.

Would Mustard SLAM/Shock level finish things up for us? Thanks.
 

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It's likely just dead algae, or even just dirt blowing into the pool (though there being less of it as you go on makes me think the former). Check the back of your weir door and the foam to see if anything is growing there. Are there any lights in the pool? I don't see any in the photos.
 
So that's the thing, as I understand it algae is microscopic and we can't see it at all - only what appears to be dead algae accumulating in the cracks/low spots of the vinyl. We do think it is dead algae (as when you brush it or even while vacuuming it poofs up into the water and disappears). I have been scrubbing the back of the weir door for a couple of days. What do you mean by foam? Worth it to move to mustard shock level?

No lights or anything else in the pool. I feel like its still algae due to the "poofing" when brushed. Is there a chance its coming from algae in the filter/heater/vision system which is not getting brushed?
 
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Mustard algae is slimy and grows and sticks to the sides of walls and pool surfaces. It has more of a yellowish green appearance. What you're describing sounds more like dead algae to me as well. That aside, would not hurt to raise FC mustard algae level for 24 hours.
 
poolguy2022 said:
So that's the thing, as I understand it algae is microscopic and we can't see it at all - only what appears to be dead algae accumulating in the cracks/low spots of the vinyl. We do think it is dead algae (as when you brush it or even while vacuuming it poofs up into the water and disappears). I have been scrubbing the back of the weir door for a couple of days. What do you mean by foam? Worth it to move to mustard shock level?

No lights or anything else in the pool. I feel like its still algae do to the "poofing" when brushed. Is there a chance its coming from algae in the filter/heater/vision system which is not getting brushed?
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The back of a weir door typically has something to help it float up to the level of the water. Usually it's a piece of styrofoam meant to be in the pool. If you can remove the weir door, check out the foam and see if it has any algae growing around it.

I don't see how moving to mustard shock level will help much. You are already chlorinating enough to kill anything short of mustard algae, and mustard algae would be visible and need to be scrubbed - if you don't see it, then it's not likely to be mustard algae, to my understanding.

Algae can't grow without sunlight, so it really can't be in the filter/heater/etc. - except the dead stuff.

Can you fill out your signature with your equipment info? What sort of filter do you have?
 
Sig should include everything now.

Ok, just checking, I can't "see" any algae at all. All I'm able to see if the remnants of what appears to be dead algae. There is no sliminess, green or yellow anything, just the dead algae in cracks. I'm not sure what else to clean. Does the order of vacuuming and brushing matter? I typically do this process in the evening: vacuuming the entire floor (not just the spots I can see with dead algae), then brushing everything - walls, floor, stairs, and inside the skimmer. I'm not sure what I'm missing to finish this off.
 
I wonder if some of the dead algae is getting through the filter. Have you done a deep cleaning of the sand at all recently? Here's the info on that:

Deep Cleaning a Sand Filter

This post will walk you through the anatomy of a sand filter, and then provide a video at the end for how to deep clean your sand filter. The filter used in the photos and videos is a Hayward S180T top mount sand filter. The images are of a similar filter. Obviously not all filters are...
www.troublefreepool.com www.troublefreepool.com

I had this happen to me too, and then did the deep cleaning and it seemed to stop.
 
I haven't deep cleaned the filter but I just changed the sand (due to thinking the laterals may have been broken). So the sand is brand new in the filter (everything I had in there was flushed out in the process and new pool sand was added back in). I did this before the SLAM started about a week and a half ago. Do I need to be wasting out the dead algae instead of filtering it at night?
 
I should also note that the water is crystal clear. There is just a little dead algae, or so it appears, accumulating in low crevices overnight. By the end of the day there is more in those crevices but hardly any in the morning. Which I guess would make sense if the algae isn't active/affecting anything at night.
 
The filter should catch it.

Keep in mind that it could be just some dirt blowing into the pool too.

Ultimately it's your call. If I were in your situation I'd keep up the SLAM a bit longer, especially if you're getting less each day. At some point you could call it done and just keep FC elevated. I don't think raising to mustard algae levels will really help, though. I guess it is OK to do it once and see what happens, but if it is mustard algae and you're not brushing it because you don't see it, it might not really help either.
 

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Here's the weir door. I took it out and scrubbed it and put it back in just now. There appeared to be some black stuff on it, but nothing substantial it seems.
 

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That last photo looks like it may have something on the foam. Did you scrub it with some diluted liquid chlorine? Might be worth doing to be sure.
 
Alright so here is an update over the past week. We ended up seemingly getting rid of the brown spots... but only for it to reappear a day or so later. Our CYA lowered (due to water displacement) to 40 and we have been maintaining mustard shock level (~24ppm) for about 4 days in hopes to superchlorinate and kill any algae. Yesterday we woke up and there was nothing in the pool, we were so excited! Later in the day though, we noticed some in the lower areas/cracks. So we vacuumed the floor to waste, refilled some water and brushed and scrubbed everything again last night. Algae wouldn't come from a well right?

This morning we noticed a small amount in the cracks as well. When we woke up the FC was at 23 after chlorine being added to get to ~26 in the evening.

Should we see no loss in FC overnight at mustard shock level or could there actually be some loss?

Does it make sense to maintain this at mustard shock level (not just SLAM level)? We are vacuuming to waste the floor (quickly but so it doesn't end up in the filter and potentially just meander its way back into the pool), we're scrubbing everything from the deck surface everyday as well too. We added 1/4 cup of DE through the skimmer into the filter last night as well in hopes that if any suspended algae/dead algae make its way into the filter it will be caught and not thrown back into the pool.

Is there anything else we can do to improve this? Anything else we can try (sodium bromide or something else)? Our pool seems to be completely clear otherwise with this small amount of accumulation in the lower crevices of the liner.
 
If you’re losing overnight it’s due to either testing error or algae. The former isn’t too likely and the latter is. Have you checked all the other nooks and hiding spots? Any lights in the pool? Ladders, main drains?
 
As far as I can tell we have scrubbed everything everywhere. We really don't have much in the pool, the stairs are built in, no lights, no main drain. We clean the skimmer area and well around the steps.

What about phosphates? I'm reading that phosphates are the food for algae and if I'm not mistaken my TF-100 test kit doesn't test for them. Is that a possibility? Any other thoughts?

Thanks.
 
Phosphates don’t matter if you don’t have algae. Doesn’t matter if you set out an all-you-can-eat buffet if you don’t have guests to eat it. That said, some do lower phosphates for insurance - but it’s not something strictly needed for pool care. See link:

Phosphate Removers - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
Reading through this TFP post suggests (JoyfulNoise post) that maybe for myself (with a well with lots of iron) maybe a reason or two to at least consider phosphate removal. I understand your analogy, essentially saying we still have something growing. Is it possible that this dead algae is passing through the filter anyway? Or is it more likely that its new dead algae from within the pool and has nothing to do with the filter?
 
It might be worth inspecting the sand bed. I know it’s new but maybe check and make sure nothing crazy is happening in there by running a hose and pushing it gently into the sand bed to check.

If you’re losing FC overnight then the FC is killing something…so long as your night testing is after sundown and morning test is before sunrise.
 
Wanted to give an update as we're nearing the end of the season -

We did have algae, and we did eradicate it using the SLAM method. We did mustard algae SLAM (significantly higher chlorine levels) for at least a week after the regular SLAM. We threw everything in the pool as directed, (toys, brushes, noodles, tubes, etc.) and everything got eradicated. We do occasionally get stuff that looks similar in the pool now - but now its just sand, not sand & algae.

What a difference it has been! We have had crystal clear water using the processes/chemicals recommended from this site, pool math to sort everything out and buying only what we need. It has been such a huge improvement to what we had last year. We throw a robot cleaner in whenever we get bugs or sand in the pool and within a couple of hours its perfectly clean. We can tell that our pool is much clearer than it has ever been, the floor and steps are no longer slippery (algae) and the water just feels better - not sure how to describe it. This summer has actually felt like we own a pool, not another headache.

Thank you to everyone for the support - this place is fantastic.
 
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