Brown spots/circles on glass

[Nelson]

Next day after cleaning the glass they are back: brown spots

They are:

- round shape

-brownish color

- very hard to remove, need brute force like coraline algea.

 

Not sure what it is and how to prevent it. Sorry for the blueish photos!

 

[FISHnChix]

I don't know what type of alage it is but I get it too. Get a mag cleaner with a scrapper.. I use nano flipper.. you will be amazed how easliy it comes off!!! For months when I first started I was scrubbing that crap off during wc and like you said it's a MF to get off..