Turning the corner on mustard algae?

[Sandra B]

(18,000 freeform in-ground plaster, Pentair Triton II sand filer, Jandy pump and SWG, all about 6yrs old except I replaced the salt cell last summer. Just added borax to 50 to help the PH drift)

Hi everyone! I've been a BBB convert since about 2 years ago when I discovered this website with a new (to me) pool, and you all helped me through the chemistry. Thanks to you, I've had a clear sparkly pool for 2 years with zero pool store additions! Yay! Except...

I'm in Louisiana so we don't "close" pools for the winter. My pump/SWG runs its normal 8 hrs/day/winter except if the water temp gets below 42 it automatically turns on and runs until the water warms a bit. Keeps things from freezing. Seldom does this happen; we just don't get that cold very often. Pump and in-pool Legend vacuum are on timers so no work to do there, 1 hour automatic daily vacuum. I don't have a heater so no swimming from about October til late April when it heats back up. (Admission coming up) Sooo, during the winter I didn't check things as often since, well, it was winter and everything is on timers, just checked chlorine occasionally keeping it around 5 for CYA of 65, and adding MA when needed. Cleared baskets around weekly. Didn't brush much ,and SWG was dialed down for less sun but kept up with the 5 CL just fine. Pool sparkled all winter.

The problem: Last summer I noticed some "sand" on my built-in steps and on a ledge, mostly around the elbows. Swept it off almost daily, it would be back the next day. I have flagstone around the pool and thought it was getting grit in thru rain, etc. Really mostly just ignoring it. Water temp can exceed 100F in summer (ya, it's hot!) The sand persisted all winter. Ignored it, swept it off occasionally. As I started swimming again in May, I started paying more attention to it. Finally a couple weeks ago I "captured" some in a mason jar, based on some reading here, and let it settle. It is not sand. Fine yellowish dust. I nuked it with bleach in the jar but couldn't really tell a difference. It brushes to a poof into the rest of the pool, but the next day it's back on the steps. Did not poof when I brushed the bottom. Since it persisted all winter, not pollen.

I started a SLAM last week after balancing TA (a little low at 50, moved up to 70ish) and pH. CYA I rebalanced about 65. Will take to 70 after SLAM. CH is 330. CC has been zero all winter and still is. During the SLAM I have maintained zero CC so I thought I was barking up the wrong tree, but I've since read threads that MA may not impact CC like typical algae does. I'm on day 4 of the SLAM and MIRACLE OF MIRACLES there is no buildup of MA on the stairs or ledge, for the first time since last summer! However, there is still a slight poof when I brush the stairs, and now there is slight poofing on the pool bottom and I can see the MA slightly move along when I brush the bottom.

My questions: am I killing this stuff? Is the fact that the stairs are now clear a good sign, even though I can now "see" it when I brush the bottom? Am I now brushing the dead algae off the bottom, and that's why it's there now? I also deep cleaned my filter with partial success (that's another thread) and I have some celluose to use if that would be helpful (never used it before).

How will I know when to stop SLAMming? My chlorine holds all night, and no CC. Drops during the day since I have the SWG turned off during SLAM (water temp is low-mid nineties, full sun, outside temps in the 90's). Pool is clear yet still poofs when brushing (minor poofs, no buildup). I'm thinking I slam another day, then go all MA SLAM on it for 24 hours, then drift back to normal, turn on the SWG, and see what happens. Thoughts? Am I doing this right?

 

[Patrick_B]

Welcome aboard! Glad you decided to post.

Just remember, when you pass ALL three criteria for SLAM, is when you have confidence that you are done with the SLAM. Mustard Algae is a little tougher and takes longer sometimes so make certain it is all dead before you complete the list.

 

[zea3]

Are you only seeing it collect on the steps and the flat areas of the pool? Does it feel slimy when you rub it between your fingers? How long and when do you run the filter? Since you are holding FC overnight I think what you are seeing is deterioration of the sandstone. These days builders only recommend using very hard stone with a SWG, and some builders will not use any stone with an SWG. Sandstone is very soft and slowly dissolves with exposure to saltwater. Sealing the stone and rinsing the deck after there is a lot of splashing can help preserve the stone.

 

[astronaut888]

I have the exact phenomenon on my steps and have always thought it was, in fact, sand.

I have never detected any CCs and have performed a couple of OCLTs recently for good measure with no loss.
Water is crystal clear and good to go.

It is strange how it collects no matter how well or frequently I brush and vacuum the pool

I have always attributed it to my dogs who tend to "cool off" periodically on the steps - even though it seems to collect even when I don't think that they have been in the pool at all.

Is the consensus that this "sand" is, in fact, mustard algae??

I fought mustard algae YEARS ago and have no recollection of it looking like sand.

 

[Sandra B]

Are you only seeing it collect on the steps and the flat areas of the pool? Does it feel slimy when you rub it between your fingers? How long and when do you run the filter? Since you are holding FC overnight I think what you are seeing is deterioration of the sandstone. These days builders only recommend using very hard stone with a SWG, and some builders will not use any stone with an SWG. Sandstone is very soft and slowly dissolves with exposure to saltwater. Sealing the stone and rinsing the deck after there is a lot of splashing can help preserve the stone.

Yes, only the steps and a flat ledge. 90% of it in shallow end, the wide flat steps you see in the photo. It does not feel slimey, only because you can't really "feel" it--it poofs away. Can't pick it up with your hand--I used a widemouth mason jar and a paintbrush to sweep some in the jar, although sweep implies it actually sweeps instead of poofs--it poofs only. During summer I run the pump 12-14 hrs/day, about half that during the winter months. It runs during daylight hours, off at night. During SLAM it's running 24 hrs. I initially thought it was sandstone grit, which it why I just watched it and swept occasionally for a year. But there is zero grittiness to it, and now that Day 4/5 of shock was made it disappear, I don't think it is sandstone. I really think it's an algae. Thanks for your thoughts...I think sealing my sandstone is a good idea either way.

 

[HouTex]

Are you only seeing it collect on the steps and the flat areas of the pool? Does it feel slimy when you rub it between your fingers? How long and when do you run the filter? Since you are holding FC overnight I think what you are seeing is deterioration of the sandstone. These days builders only recommend using very hard stone with a SWG, and some builders will not use any stone with an SWG. Sandstone is very soft and slowly dissolves with exposure to saltwater. Sealing the stone and rinsing the deck after there is a lot of splashing can help preserve the stone.

That's what I thought as well. Sandra B, have you closely inspected your sandstone coping to see if it's showing any signs of deterioration?

 

[Sandra B]

Astronaut, what you have sounds like what I have, and my ONLY indication that it is algae is that I have shocked for 4 days and it is GONE, for the first time in over a year. If you're like me, you've been noticing and sweeping this off the stairs daily (sometimes not sweeping daily, but noticing) and thinking it was odd but not a concern--dirt, grit, pollen, whatever. Until it disappeared yesterday, and did not reappear last night or this morning, I would have said some kind of dirt. I have been resisting the Mustard Algae diagnosis, but I can't make anything else fit my fact pattern that would pick yesterday as the first day in 12 months not to appear...

Thanks!
Sandra

 

[astronaut888]

Astronaut, what you have sounds like what I have, and my ONLY indication that it is algae is that I have shocked for 4 days and it is GONE, for the first time in over a year. If you're like me, you've been noticing and sweeping this off the stairs daily (sometimes not sweeping daily, but noticing) and thinking it was odd but not a concern--dirt, grit, pollen, whatever. Until it disappeared yesterday, and did not reappear last night or this morning, I would have said some kind of dirt. I have been resisting the Mustard Algae diagnosis, but I can't make anything else fit my fact pattern that would pick yesterday as the first day in 12 months not to appear...

Thanks!
Sandra

I'll try and grab a photo tonight - it sure looks like what you had in your specimen jar!()

 

[Sandra B]

That's what I thought as well. Sandra B, have you closely inspected your sandstone coping to see if it's showing any signs of deterioration?

I'll take a close look after work today. The coping can feel a bit gritty when walking on it barefoot, but not inside the pool, and I still can't get over how the "grit" has miraculously disappeared from my stairs after 4 days of slamming. It has been there every single day since sometime mid-last summer. It is not there anymore, as of yesterday. That's what makes me think it's not from the rock. And it is only in 2 places--the step and the ledge. Does not collect anywhere else in the pool, though the sandstone goes all around. The steps are in the shallow end, the ledge in the deep end. I'll take a close look later today, thanks!

 

[zea3]

Keep an eye on it and see if it comes back after you drop to normal FC levels.