I have several goldfish tanks and each one has developed what I presume is
brown algae on the sides of the tanks and on some of the artificial plants I
have in them.

I change water about every two weeks because all the tanks are overstocked.
I scrub the algae off but it keeps coming back.

Should I treat with something or is this stuff harmless Looks like heck
though.

Thanks,

Tom in Howell, NJ