I'm in a submarine & hear it "could" have a leak--> most my priorities have already changed..... Also curious as to why it's questionable and yet still hasn't caused any adverse effects in anything yet. >>
He's just trying to identify what it is.I don't understand why this is in question? It isn't like it's going to rust even if it is pyrite. I see exactly what you are talking about, but it looks way blurry and way white. I wouldn't worry about it, I am sure there are places in the world where pyrite occurs naturally in fish habitats without any problems at all. After all it isn't like you found a piece of nuclear waste floating across the top of your tank.
He's just trying to identify what it is.
Enclosed system isn't comparable to open & running waters.