Black staining on new plaster upon adding chlorine - what is it?

[InheritedAnthony]

Hi!
We recently got our pool replastered with Diamond Brite (Oyster Quartz). After an acid-hot start, we balanced the pool water and added chlorine.
The water was acidic for about a week as the pool guy ghosted us & we had to find a new person.
The pool guy added a lot of chlorine with pucks, about 8ppm.

Within a few days of the chlorine being added, I noticed a new ugly black stain forming under the old original Anthony light fixture, see attached.
The contractor had not replaced the working light and just plastered around it.
Any ideas on what it could be and what treatment options are?

We also have some black staining on the grout of the new tiles in one small area - any advice?

On another note, we had a bunch of brown stains before we added chlorine from berries and leaves falling into the pool and sitting in one place while the pump was off. Most of those have disappeared since added chlorine but some stayed and are fading slowly. Will those fade more over time or is there a manual spot treatment I should consider?

Current Chemistry:
FC 7, CC 1.5, 8.4 PH, 100 TA, 150 CH, 5 CYA

 

[ajw22]

Put a paste of crushed vitamin C tablets in a sock and rub it on the black stains. If they lift then it is iron stains from rusting of your pool lights.

 

[InheritedAnthony]

I'll try that.
any way to make it stop after if it is Iron?
Or do I need to find a way to replace the whole housing?

 

[ajw22]

I'll try that.
any way to make it stop after if it is Iron?
Or do I need to find a way to replace the whole housing?

Remove the light and see what is going on in the light niche.

Did they remove the light from the niche when plastering?

 

[JamesW]

The light looks like it is ruined.

It looks like it is half filled with water.

The black is probably from copper from the light niche or iron from the light due to the acid.

I would plan to replace the light and clean out the niche as best as you can.

 

[InheritedAnthony]

Remove the light and see what is going on in the light niche.

Did they remove the light from the niche when plastering?

I don't think they did.

The light looks like it is ruined.

It looks like it is half filled with water.

The black is probably from copper from the light niche or iron from the light due to the acid.

I would plan to replace the light and clean out the niche as best as you can.

The light still works, but it may well be ruined. unfortunately, it's an obsolete Anthony light that I can't easily replace without replastering that section of the pool, which will be frustrating as we just plastered it.

I still need to give the stain a Vitamin C scrub to see what happens.

 

[JamesW]

The light is probably unsafe and I would recommend that you disconnect it from power.