Black spots... Black Algae or Metal Stains?

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S

smohun

0
May 18, 2017
30
Leonardtown, MD
Pool Size
21000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Truclear / Ei
This is my third season with our new pool, and we have some small black/gray dots on the sides of our plaster walls. We noticed some last year, and the company that installed the pool came out and identified it as black algae. They tried the chlorine tablet test and that didn't fade at all, so I think they just gave up and said it's black algae. I've researched everywhere and tried everything. I tried to scrape some off, but there is nothing raised to scrape off. I also did the chlorine tablet test, which didn't do a thing to fade the spots. I did apply Vitamin C and the dots disappear, but it leaves a bit of a grayish stain on the plaster. Should I try to slam and treat for black algae, so it doesn't get any worse or should I assume it's metal and treat it for that? Has anyone had a similar issue? Thanks in advance!!!

FC: 5.0
CC: 0
PH: 7.4
TA: 110
CH: 290
CYA: 60
SALT: 3200
IRON: .1
TEMP: 63
 
The plaster seems smooth to me. I'll try tomorrow for a picture, it was too windy today when I tried. My Taylor test kit doesn't have a copper test, so I had the local pool company do a free water test and it came back as 0 for copper. But maybe that's not accurate? I don't trust any of the local pool companies, and would like to solve this myself without messing it up.. since I'm a novice pool owner. Thanks for your help.
 
It appears to only be on the walls. In some places, it seems like the dots are in a line. We thought at one point that the automatic pool cleaner wheels were leaving marks.
 
The light in the deep end doesn't have any and I don't have metal steps. I don't see any other corrosion except the screws in the floor returns look a little dark, not sure if that could be rust? I've never noticed a start current, but last year was my first full season. I did manage to get a picture. Thanks for helping. 20180430_182339.jpg
 

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No cracks that I can see. Yes, odd pattern...like I said earlier, I thought maybe the automatic pool cleaner was making the marks with the wheels. Is there any harm in treating it for metals, to rule that out?
 

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Ok, will look for a crack. The vitamin c tablet rubbed on it will make them disappear, but it leaves a gray stain. I don't want one stain and make another. In my desperation last year, the local pool company recommended ascorbic acid and another recommended Pool Stain Treat to remove the metal stain. I didn't buy anything then, I just didn't want to do anything that's very hard to reverse.
 
Could copper be in the pool and not show up on a test? I didn't identify any, but I did have .2 of iron.
Any suggestions on first steps to fix the problem? Thx again.
 
If most of the copper is in stains, then there won't be much in the water to register on a test.

I think that the line is relevant. Maybe a crack with metal bleed through from rebar. But, that would be iron.

The vitamin C test seems to match copper.

Since vitamin C leaves gray, it probably wouldn't give good results.

Sulfamic acic (Jack's #2 copper and scale stuff) would probably work better but it has it's own issues, like creating lots of combined chlorine for weeks.

You can try some sequestrant, but I don't think that it's going to be really effective.
 
Thanks James. I don't see any cracks and these dots are more plentiful on the either side of the pool walls with similar and different patterns. I guess I can start with the Jack's product, and go from there. Thanks for your help and please let me know if you think of anything different that would help.
 
Should I rule out black algae by doing a slam? If so, should I do that first or try Sulfamic acic (Jack's #2 copper and scale stuff)? Thanks in advance!
 
Black algae wouldn't respond to vitamin C. Black algae is a lot like black mold. If it was black algae, you should be able to scrape some off for examination. Black algae is a blue/green bacteria. If you scraped some up, it would be a soft blue green goop.

I really am not sure what it is. I'm thinking that it's probably copper. But, I don't know why it would be in a pattern like that.
 
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