Anaerobic bacteria or just algae? (gas bubbles scare me)

[Claybo]

I’m a new fish keeper of about 4-5 months (+about 3 months of research) and I have apparently put one of my large sponge filters up against the glass right next to a window I leave open to give my plants morning sun. I just stuck my head between the tank and the window and notice the part of the sponge filter I couldn’t see is completely green and filled with a few large bubbles. My first thought was it being algae and oxygen bubbles but then I had the thought that maybe there is not oxygen getting there and it’s possibly anaerobic bacteria that could be producing ammonia and sulfur gas bubbles right? I’m sure I’m being totally paranoid but if someone can confirm that I will not kill everything in the tank with sulfur if I pull the sponge off the glass. 

I plan to just leave it there if it’s not an issue because I really don’t mind algae and other little natural parts of my tank as long as it stays manageable.

[nabokovfan87]

When the algae gets very dense light that it can create anaerobic bubbles.  I would scrape it and make sure any fish/shrimp aren't around when you do so. 

That reason is why I will scrape the whole glass on the tank every few months.  If you have a pleco to keep things under check that's one method, but it looks like the foam is right up against the glass. 

Welcome to the forums 🙂

[Claybo]

Yeah it is right up against the glass, I’m a dummy. Thanks for the advice. I’ll probably have a friend hold my water change tube right above it when I pull it away and scrape it. I haven’t had to scrape any algae yet because I have a lot of plants and have had very low bio load.