Help - Brownish Algae Stains On Tank Sides

[fishnovice]

A small plastic tank that was near a sunny window has developed patches of horrible brownish green, almost like rust stains, on tank sides and the fine gravel is turning brown in places too,( It's the bright orange kind of fake gravel that came with the tank.) The brown is a very thin layer, not raised or slimy more like a stain than algae growth. It's in large irregular patches too, doesn't cover the whole tank sides.

Transferred fish to another tank in case it was harmful and emptied half the water. Tried to remove brown stains but it doesn#t rub off easiiy with sponge. Worried about using steel wool or similar as tank is plastic.

What is this brown stuff, does it harm fish and how do I get rid of it?

Thinking of having a proper tank clean as it's just a spare/quarantine tank. Boiling the gravel should kill what ever it is, but how do I remove stains? Should I use bleach to kill it and if I do,will traces of bleach in tank harm fish if I use the tank again at some point?

 

[dcarmor927]

A Picture would be a lot of help, im not an algae expert but i know that a pic would be better. I had a similar occurrence in a tank and was told that the stuff was "diatoms". i've since torn that tank down, but in my 55 gal i had something similar again, but my new pleco takes care of it. If in fact it is just diatoms, they are harmless to your fish

 

[hypno_pleco]

the alagae wont be bad for your fish, but all the same you dont really want it there.
the tank should of not been near a sunny window, if it is near a sunny window then its inevitable that you WILL get algae,
if it was me, i would move the tank away from the window, and clean out the tank with a sponge maybe, if not an algae scraper,
then make sure you never let the tank see direct sunlight, otherwise it will come back