Rust colored Algae, or localized Rust?

There is an orange splotchiness on the inside center front of my fishtank,
which looks almost like rust. My Pleco hasn't touched it, although all of
the other tank walls are clean.

It occurs to me that this is in roughly the same area as my Black-lite spot
lamp shines down on the top. Can there be a relation?

What is this crap? Is it dangerous? What's causing it?



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The power of accurate observation is often called cynicism by those who have
not got it.
-George Bernard Shaw

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