In my opinion, the lightning hypothesis doesn't hold up. There's no known correlation between lighting and this type of reaction, there's no evidence that the pool was hit by lightning and there's no logical reason that lightning would cause it.
An electrical issue is more plausible because a stray current can cause metal corrosion and staining. However, you would need a source of metal.
Based on the filter, it doesn't look like copper or iron. It might be silver or manganese or maybe zinc.
The pattern in the pump basket and the filter suggests that it was something in the water that was insoluble.
It kind of looks like the ruthenium oxide coating that's on the titanium cell blades but that stuff is very unlikely to come off.
Maybe check cell blades for missing black coating.
In my opinion, some sort of black dust got in the water but I don't know what it could be.
Do you have surveillance video that you can review?
If you wash down the cartridge, does the black come out?
No neighborhood fires nearby?
An electrical issue is more plausible because a stray current can cause metal corrosion and staining. However, you would need a source of metal.
Based on the filter, it doesn't look like copper or iron. It might be silver or manganese or maybe zinc.
The pattern in the pump basket and the filter suggests that it was something in the water that was insoluble.
It kind of looks like the ruthenium oxide coating that's on the titanium cell blades but that stuff is very unlikely to come off.
Maybe check cell blades for missing black coating.
In my opinion, some sort of black dust got in the water but I don't know what it could be.
Do you have surveillance video that you can review?
If you wash down the cartridge, does the black come out?
No neighborhood fires nearby?
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