Please help. I have two tanks - a 5gal in which I have a Betta, and a 40gal which houses two comets, 3 common goldfish, 2 calicos and a dragon eye and two algea eaters (the smaller of the two used to be in with the Betta until he was being nipped at). In both there are brown spots on the walls of the tanks and the same "stuff" is starting to cover the rocks (I have some small glass (I think) bobbles also in the 5gal). I've done my weekly water changes to see if it would help - it didn't! I've taken one of the bobbles out of the 5 gal to see what was covering it. It has the consistency of mud!? The 40 gal tank is several months old and the fish are doing well. The 5 gal is only about two months and the Betta seems to like his new bigger home (he was in a bowl - I know, I know and I'm sorry! ) Can anyone help me solve this delima? My nitrites and ammonia are zero.

ITs Brown Algae hun. Very common in the fish tanks, nothing to worry about just get an algae scrapper and wip it off.

yeah i had brown spots like you when i did my weekly water change i took my alge brush or scraper came clean no problem

Yup...
That's brown algae...just wipe it off with an algae scrubber...if it's on the gravel, when you do your water change, agitate the gravel, then vaccum.

Thank God! I thought it was something serious!