Wall Black Stains

[djpool21]

I've been dealing with black stains or discolorations for a 1-2 years mainly on 2 walls. I don't believe it's black algae but I don't know what it is or where it's coming from. It's not irregular or patchy black stains and they don't smear or wipe off. The only treatment I've done is occasionally brush the areas with a stainless steel brush. This reduces the discoloration slightly but it never goes away.

It's very confusing because I can be in the pool and depending on the angle I view it and sun, etc. and I'll think the areas have not worsened over time. But at other angles it seems worse. I remember 3 years ago when the pool was built I saw some of this staining by the light fixture. PB is now deceased and gave some BS answer for the developing stain. I know for certain that it's worse than it was 3 years ago. The stain by the return is newer and appeared this year. I saw a darkening in the spa by a jet developing and I was able to brush it away with a nylon brush.

As you can see from the pictures (sorry about my reflection) there are mainly 2 stained areas. The largest area is between a light fixture and pressure side hose fitting and the other by a return on an adjacent wall. They are not near each other. I don't use a copper based algaecide or sanitizer. However, PB originally installed a Nature2 which I removed the cartridge after 4 months of usage in 2021. Strictly Trouble Free Pool methods used since then. Fill water is softened well water and rain. CSI is managed from slightly negative to 0.

Water Test Results from Taylor K-2006 (except for Borates):
FC: 10
CC: 0
PH: 7.8
TA: 70
CH: 360
CYA: 50
Salt: 2800
Borates: 15 (I've discontinued use this year)
Approx. Pool Temp: 55 degrees

I'll try to take better pictures without my reflection. Thanks for your suggestions to help resolve this mystery!

 

[ajw22]

Stain ID Kit | Jacks Magic

jacksmagic.com

Take your pool water into a pool store and have it tested for metals.

 

[djpool21]

Per Leslie's my Iron is 0 and Copper is 0.2. I'll have to wait until the water warms up to at least 65-70 degrees to use Jack's test kit.
If Leslie's copper test is accurate, is 0.2 too high and could it cause staining? Is this level of copper fairly typical?

 

[ajw22]

Copper in Pool Water - Further Reading

www.troublefreepool.com

0.2 copper is borderline since the test only shows copper in solution in the water and does not show copper already deposited on your walls. So you could have had more copper in the water before some of it got deposited.

Where does your fill water come from?

 

[djpool21]

Copper in Pool Water - Further Reading

www.troublefreepool.com

0.2 copper is borderline since the test only show copper in solution in the water and does not show copper already deposited on your walls. So you could have had more copper in the water before some of it got deposited.

Where does your fill water come from?

Thanks Allen. I never had a problem with obvious copper staining even during the short time I had the Nature2. I never used any "blue" chemical products that could have introduced copper. During that time I also had Leslie's test my water and copper was either 0.0, 0.1, or 0.2. It was never above 0.2. Same results with iron. Fill water is softened & filtered well water and rain. I don't know the level of copper in my fill water.

 

[ajw22]

I don't know the level of copper in my fill water.

Take your fill water to Leslie and tell them it is new pool water.

 

[JamesW]

I never had a problem with obvious copper staining even during the short time I had the Nature2.

Nature 2 adds copper.

Copper tests are very unreliable.

Also, most of the copper can be on the plaster as stains and this will not show up in a copper test.

Black algae is easy to diagnose because you can scrape it off and it is like black mold that it soft and spongy.

 

[JamesW]

If 90% of the copper in in the form of stains, then any copper test will only show 10% of the amount of copper that is in the pool (Assuming the copper test is accurate, which it usually is not).

So, a reading of 0.2 would really be 2.0.

 

[JamesW]

Get the stain ID kit.

The black does not look like black algae.

Stain ID Kit | Jacks Magic

jacksmagic.com

 

[djpool21]

Thanks for the suggestions. I tried vitamin C in a sock on a couple stained areas and it had no effect. I had Leslie's test my fill water and the test showed 0 iron and 0.1 copper. They also tested my pool water and it had the same metal results as the fill water.

I'll have to wait to next spring for the water to warm up in order to use Jack's Magic stain ID kit.

 

[ajw22]

I had Leslie's test my fill water and the test showed 0 iron and 0.1 copper. They also tested my pool water and it had the same metal results as the fill water.

A pool water test only finds metals in solution in the water and not any metals that have deposited on the pool surface. If the metals have left the water onto the surface your pool water can test low for metals.