Black Algae or Something Else?

[Redstar7t]

Hello,

I have another thread here needing some desperate help identifying stains that have been popping up this year. They are very small speckled brown spots that are showing up around the pool (plaster), mostly on the floor and mostly around the edges. Everything I read tells me I have black algae but the only reason I'm hesitant is because this past spring I had my pool deck ripped out and repoured with a brown colored concrete, same color as these spots. These spots rub off easy with a pumice stone though do still leave a lighter brown mark underneath.

I have tried rubbing a chlorine puck on them with no change, and I've rubbed vitamin C paste in a sock on them with no change. The picture of the tile I've attached shows an example of how some of the concrete around the existing tiling is crumbling off where they overlapped the concrete on the tile, not a big deal to me aesthetically but I can't help but wonder if these bits of concrete are falling off and somehow attaching themselves to the plaster? I wanted to get your thoughts before I go into black algae fighting mode..

Another reason I question black algae is that I've kept pretty consistent params (SWG pool):
8-9ppm FC
70 CYA
7.5-7.8 pH
100 TA
250ppm calcium
3300ppm salt

 

[Rancho Cost-a-Lotta]

I'm no closer to guessing what it is than you are. However, I don't believe it's black algae. If you look at a couple of the photos, I think I see what appear to be comet trails coming off of the main stain. If those comet trails are headed downhill towards the deep end, it means whatever was there was allowed to sit on the surface and then began to dissolve and stain downhill. I've seen this with tannin stains that are left behind by seeds from a tree, fertilizer granules and metallic items. Do you see those comet trails?

 

[Rancho Cost-a-Lotta]

I should have asked, but have you tried to collect a sample of the substance? Try scraping some up with your fingernail and wipe it on a white piece of paper or napkin. If it smears green, then it is black algae.

 

[Redstar7t]

I'm no closer to guessing what it is than you are. However, I don't believe it's black algae. If you look at a couple of the photos, I think I see what appear to be comet trails coming off of the main stain. If those comet trails are headed downhill towards the deep end, it means whatever was there was allowed to sit on the surface and then began to dissolve and stain downhill. I've seen this with tannin stains that are left behind by seeds from a tree, fertilizer granules and metallic items. Do you see those comet trails?

I see it on some of the spots, actually the spots more towards the middle of the pool have comet trails. I'm wondering if I'm dealing with two different things. I might start with a SLAM and see if any of these go away

I will try the scrape and smear method tomorrow..but just from my experience scraping this stuff with the pumice stone I think it's either: not going to scrape off at all, or: immediately dissolve into dust into the pool and I won't be able to collect it on my fingernail or anything

 

[Rancho Cost-a-Lotta]

Yeah, it's tough to do a diagnosis with photos. Are the areas where you're seeing the black spots pitted or delaminating? The only experience I've had with black algae is at my parents home. The plaster was about 50 years old and was pitted very badly. The black algae would only grow in these pitted areas.

 

[Rancho Cost-a-Lotta]

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

 

[Redstar7t]

Yeah, it's tough to do a diagnosis with photos. Are the areas where you're seeing the black spots pitted or delaminating? The only experience I've had with black algae is at my parents home. The plaster was about 50 years old and was pitted very badly. The black algae would only grow in these pitted areas.

I'm a little more convinced that at least some of it is black algae. Some of the bigger spots are indeed inside little dime sized holes/pits in the plaster, I have about 4 of them in the deep end. They're not very deep holes but just deep enough that the scrub brush doesn't get to it very well.
I'm going to continue the black algae fighting routine but I'm wondering if I should fill in these holes with some sort of diy plaster fix that can cure underwater. Would this be a dumb idea? Thoughts? Could I fill them in with the black algae underneath?

 

[Rancho Cost-a-Lotta]

but I'm wondering if I should fill in these holes with some sort of diy plaster fix that can cure underwater.

@AQUA~HOLICS or @1poolman1 may be able to advise...

 

[AQUA~HOLICS]

The plaster patch would most likely not adhere to the black algae, it requires a more stable surface.
Filling the void with a plaster patch after the black algae is completely removed would remove the void that gives the black algae an area to grow.

 

[Redstar7t]

Yeah, it's tough to do a diagnosis with photos. Are the areas where you're seeing the black spots pitted or delaminating? The only experience I've had with black algae is at my parents home. The plaster was about 50 years old and was pitted very badly. The black algae would only grow in these pitted areas.

Had something really interesting happen that can hopefully tell me what this is, I went down to the little "holes" to scrape them with a small wire brush to break the heads off what still may or may not be black algae. As I was doing this I noticed yellow/brown dust coming out of the hole, followed by a decent sized clump of some sort of material that seems to be organic. It's squishy and leafy and orange/brown, it smears orange as seen in one of the pictures. I'm thinking a type of algae but not necessarily black algae?

 

[Rancho Cost-a-Lotta]

What first comes to mind for me is rust from rebar.

@JamesW may be able to help.

 

[JamesW]

Does it stick to a magnet?

 

[Redstar7t]

Does it stick to a magnet?

Just tried, it falls off the magnet pretty easily. Doesn't appear to stick to it any more or less than any other surface

 

[Redstar7t]

What first comes to mind for me is rust from rebar.

@JamesW may be able to help.

If it was wouldn't I see a reaction with vitamin C? Vitamin C does nothing to this stuff

 

[JamesW]

Maybe organic debris that got into the plaster mix.

 

[JamesW]

Hello,

I had my pool resurfaced with super blue diamond brite last fall. As I get closer to it being a year, I have a few items that I'm going to have the plaster company fix under warranty (couple small spots of spalling). I have a few questions about the nature of diamond brite as I don't know if they're problems that the plaster company should look at or not:

- The plaster has some mottling of dark and lighter blue areas, I don't really mind and think it looks good. Along with the mottling, the darker spots are rougher than the lighter spots. The darker spots feel like sandpaper while the lighter spots are smooth. The rough spots don't hurt, it's just noticeable texture difference when walking on it. Is this normal?

- In the deep end there is a long brown streak/stain that was there from the beginning of the re-plaster, I'm guessing somebody got mud on the wet plaster or something. The plaster company said this stain would fade from chlorine. Close to a year later its not really faded much. I'm guessing the stain is mixed in with the plaster. Should I have them acid wash this one area?

Thanks

Are these the same areas?

Maybe some sort of mud or other contamination got into the wet plaster mix?

 

[Redstar7t]

Are these the same areas?

Maybe some sort of mud or other contamination got into the wet plaster mix?

Nah the mottling in that post was mostly blue/white mottling that has gone away as the plaster cured.

Maybe it's mud but the plaster is now going on two years old, never seen anything like this until now. Like I said in the original post though it was this year that the deck got done, so maybe something from the deck got in.
But I also have a couple darker black spots with comet trails that have nothing to do with the "holes" I was talking about..these also react to nothing. I'm so stumped at this point

 

[JamesW]

Hard to tell exactly what it is.

I do not think that it is black algae, but I have no idea what it could be.

 

[JamesW]

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[Redstar7t]

Just an update on this...
After a slam and high FC/brushing for a few weeks I didn't see any changes. This stuff is hard and not slimy or anything like I've seen describing algae. I think I'm going to rule it out.

I did a full ascorbic acid treatment out of desperation with no changes either..

I'm wondering if it's something coming out of the plaster similar to calcium nodules. It doesn't look like calcium nodules though...still stumped
I did read something interesting about off-white "calcite crystals" that can form with low calcium. I am on the low end of the calcium spectrum at about 250ppm..I might try raising it