Help! Is this algae or what?!

[eikotsai]

Our pool wall has this super odd stain spot. It is brown like rust, and cannot be brushed off. We suspect it's algae so put in lots of shock, chlorine or algaecide, but still doesn't work. Every morning it has orange stuff growing out, and after we brush the orange stuff will be gone but later will grow back again. We even drained water and scrubbed chlorine tablet on the surface. It still didn't kill it. Can someone please help us here? We are desperate. Our pool guy said he never saw this kind of algae before.

[Teapot1]

Stop putting lots of things in, probably make it worse. Algaecide doesnt work unless its copper based and just uses up the chlorine quicker as it tries to oxidise it out of the water
Test with a vitamin C tablets on the stain to see if its a metal stain, even stains can grow fur coats of metal. Chlorine oxidises metals causing them to drop out of suspension and stain, a single patch is unusual though. With the chlorine level low try the vitamin C held on the patch.

[eikotsai]

Here are some pictures for more info.

https://drive.google.com/file/d/1tnQEuu ... p=drivesdk
https://drive.google.com/file/d/1zPdH24 ... p=drivesdk
https://drive.google.com/file/d/1jOitJL ... p=drivesdk

https://drive.google.com/file/d/1IR5U4N ... p=drivesdk

Thank you!!!

[Teapot1]

Hmm, very localised spot, not quite how I imagined from your post. Hopefully your chlorine level is down a bit from when you added a lot the other day. Please still go ahead with vitamin C tablets directly on the stain. Vitamin C (ascorbic acid) does the opposite to chlorine, which oxidises metals out of solution so they show up. Vitamin C reduces the iron to a form that goes back into solution so you cant see it. If this works you'll see the staining disappear where the vitamin C has been. My first thought is a porous finish on the pool at that point with a bit of iron, possibly rebar near the surface.

[eikotsai]

Thanks for the suggestion! I tried scrubbing the vitamin c tablet on the spot but it didn't seem to work. And now the whole surface is covered by the orange stuff. Here's the picture:

https://drive.google.com/file/d/1B1k0LV ... p=drivesdk

[Teapot1]

Very strange, see if you can take a higher resolution photo as its a bit fuzzy when I zoom in. Maybe get a sample for someone with a microscope.

[eikotsai]

Hopefully this picture is clearer:

https://drive.google.com/file/d/1S5-nsE ... p=drivesdk

It's hard to get a sample because the orange stuff is easily brushed off and goes away once touched. Without the orange stuff, it just looks like a stained spot on the plaster. Do you have any suggestion on how to collect the sample?