Localized stains not removed by application of Ascorbic Acid

[anre5180]

moved in 4 months ago. and have done 1 treatment of AA as per recommendations with 1.5 lbs of AA and 128oz (2 bottles) of the Purple Stuff sequestrant and method in TFP thread. this was during colder days about 2 months ago

yet... i am not able to lift these 2 small ones on the floor of the shallow end.

nor the big one on the side of the deep end... which makes me wonder: how the heck this one happened there. I could find explanation of something fell into the pool on the floor of the 2 small one but this big one on the vertical side wall? huh?

i spent yesterday 2h in the pool with my scuba gear and oxygen tank looking for leaks and cracks and repairing where needed.

grabbed vitamin-C tablets and directly scrubbed these spots (See pictures)... no visible difference... i was inches away from them and taking my time since i had my respirator and O2 tank so i was in no rush to surface for air. no difference :-(

is there a different local treatment you guys could recommend? weather is nice and already have all the scuba gear out...may as well give a shot to your recommendations.

pool levels have been maintained by TFP recommendations and poolmath app:

PoolMath Logs

if the pictures don't come up in full resolution: 2268x4032 let me know and i can try to upload them to my cloud and share links from there.

thank you an advance for the feedback and I look forward to a more educated and experienced suggestions

 

[Texas Splash]

I would try two things next:
1. Apply a magnet to the stains. If it tries to grab, you could have rebar behind in close proximity to the plaster's surface.
2. Apply some dry acid (in a thin sock or nylon) to the area - copper. This one seems unlikely, but worth a try if Vitamin C and magnets don't work.

 

[anre5180]

I would try two things next:
1. Apply a magnet to the stains. If it tries to grab, you could have rebar behind in close proximity to the plaster's surface.
2. Apply some dry acid (in a thin sock or nylon) to the area - copper. This one seems unlikely, but worth a try if Vitamin C and magnets don't work.

what sorts of small magnet can i purchase for this ?
i can see the rebar argument on the side-vertical-wall on the deep-end... and probably if that's the case and it exposed ... it's re-surfacing the only permanent solution? or is there any product i can apply locally to get me by?

vitamin-C definitely didnt work yesterday... i will give dry-acid a shot to the floor-shallow-end stains since it seems someone dropped something there that stayed for too long in the pool ... prior to my occupancy of course...
is this applied and then brushed in? just like i did with the vitamin-C tablets onto the stain ?

 

[Texas Splash]

Any magnet can be used, but results may vary based on strength and location (if) rebar is behind the plaster. If it is rebar, then repairing that section is the only cosmetic solution.

 

[mguzzy]

Another thing to try is rubbing it with a puck.. That's the typical test for something organic. Any chance you can get a close up underwater shot of the stains? If you've got your scooba gear out for this project I'm guessing you have an underwater camera too or a nice Nikkor enclosure... or you can take stills with your GoPro!