Diatoms??

[IchthyChris]

Brown spots growing in the corner of my nano that receives some sunlight from the window. They are not slimy and are pretty hard like coralline. Snails pass right over it without pulling any off. I'm new to this game.

 

[Sniperhank]

Not diatoms. That is brown nuisance algae. I have a similar prob cuz of one of my windows. I blacked it out, but it fell down. Keep on it or it can cause issues like choking out corals.

 

[Crystal A]

Mine usually isn't brown it's green, but I take a razor to it to scrape it of the sides. Can never completely get rid of it but I can keep it a bay most of the time. Lol

 

[IchthyChris]

It's growing on an acrylic tank. No razors! I thought the brown algae is slimy? I have no other algae in my tank other than some intentional macros.

 

[Sniperhank]

Just scrape it away with a magfloat. If you dont have one an old credit/gift card will also do the trick.