So I thought I had a quarter-sized spot of black algae and then thought maybe it was mustard algae instead since this "mustard" colored bloom seems to sprout from the black algae, but after talking to the folks at Leslie's Pools and they didn't seem to have any idea what it was, I'm completely clueless and in need of help! FYI, I normally keep my pool in good clean shape (never had algae before), but traveled a bunch this summer so I don't think I was on the ball lately.

Noticed it a few weeks ago and looked around online and started scrubbing it with chlorine tablets, added a sock of tablets to hang right around the area, and scrubbed really hard (and for long periods, like 15-20 mins) with a wire brush and did beat it down somewhat, but it keeps coming back and always has at least some "mustard" bloom rising from it.

Finally trying to beat it with super doses of chems, where I shocked the pool (using Leslie's Chlor Brite chlorine glandulars) a few days ago and they applied Leslie's Silver Algaecide (where I applied one dose 1 hr after shocking and then after 24 hrs and still seeing this "mustard" bloom I applied another dose after scrubbing the area very hard again with a tablet and wire brush). So below is a pic of how it looked 24 hrs after the first algaecide treatment, so does anyone have any idea what this is exactly? I'm going to take a water sample with this "mustard" stuff back to Leslie's later today, but thought someone out there might be able to give me a heads up. Note that the area is only 3-4 inches down from the tile line, so I'm almost at the point of lowering the water, chiseling the area out (it's not that big), and then replastering that spot (at least I think that can be easily done by a DIY, right?).

Thanks in advance for any help ...

Jim

Wow, I can't wait to see what the pros say about this one! Is that tendrils on either side or a crack in the surface?

No, it's a crack where I just now took a knife and started to get into it and broke out a lot of the "black" stuff (along with some plaster). I had to stop short of digging it all out since it seemed to slant outward and I didn't want to punch a hole through.

I wanted to let the chems have another 24 hrs, so didn't go to the pool store yet (planning on getting a sample analyzed tomorrow morning). Is it possible that this crack goes through the plaster and this is something besides algae?

It might be calcium nodules. The crack would be a place where metal stains or black algae could grow. There might be steel from rebar or one of the rebar tie wires poking through the gunite causing part of the problem.

http://poolhelp.com/handouts/oB_Calcium ... andout.pdf

http://www.poolhelp.com/onBalanceCalciu ... lletin.pdf

Jim,

If you have a "hole" in your pool wall, why don't you lower the water level and patch the hole as you have contemplated?

Putting a lot of unnecessary chemistry in your water is not a good idea. Chlorine is all you need to keep organics out of your pool but I doubt any SAFE amount of chemistry in your pool water will help much to penetrate into the crevice and be effective.

Even if you cure the issue now, it will only reoccur. I would patch the wall.

PS - you do not post numbers for chlorine but I suspect you have been low in times past.

Yeah, now that I can see it looks like a deep crack I'm think I need to chip out the crack and patch it, whatever it is growing in there (algae or a chem reaction). Anyone have any good links as to how to patch pool plaster surface?

Also, thanks for the help all ...

Wanted to add an update in case anyone has a similar issue and finds this post.

I went ahead and patched the crack with some pool cement (used Leslie's Patch-It) about a month ago and it seems to have fixed the problem of that weird growth (so I think I added algea chemicals for no reason). That cement I used even alows for underwater application, so I just etched out the area and applied it without draining the pool. I was surprised it worked so well ... hopefully it holds long term, that is.

Thanks again for all the help on this board.