See attached pic for the green slime I found coming out of the filter. Also, I have noticed a lot of dark green fish poop and instead of brown algae on the glass it just looked cloudy. What am I dealing with?
Yep, it's cyanobacteria, a bacteria not an alga. You can "try" a 4 or 5 day total blackout (no tank lights or ambient light from room &/or windows, wrap the tank in trash bags) but that often doesn't work for long.
I notice your water level is very low & likely you filter flow is slow. Vacuum out all the cyano you can, often!, clean your filter! I bet it's been a while. I sometimes get cyano with too much high window light & plants blocking good water flow. It can also be from too high or too low nitrate level & maybe high temps. Change more water, more often!
You can kill it with antibacterial treatment, but unless you correct what's allowing cyano to thrive, it will come back!
You poor soul. Looks like Cyanobacteria to me. This stuff is a real nightmare. I had it in my 10g and it was awful to get rid of. You need to identify whats allowing it to thrive. Hows your water change schedule? Feeding schedules? Lighting schedules?
So heres what I did. I spot treated with hydrogen peroxide on the affected areas. Do a large water change, then tank black out. I did mine for a week. No peaking, feeding fish, etc. Cyano lives on photosynthesis same as algae but is capable of producing its own nitrogen cycle to feed itself. You have to starve it. I also dosed Ultralite Reef Products blue green slime remover , which did a lot of the main removal.
As mentioned, you need to find whats allowing it thrive before doing this or it will come back even worse. Do lots of research on the internet to get some ideas.
Do not let anything thats been in contact with this tank touch any other tanks or they will be infected too. Mine came from an lfs infected tank. When I added my fish, i netted them in with no qt (ahh novice mistakes) and that was all it took.
Is the water level this low normally or done during a water change for the picture? Is it slimy and smells or hairy ?
If it is not in the tank, just on the filter I wouldn't worry about it, just clean it.
It's not dangerous to the fish, just unsightly. Common to happen in newer tanks and unplanted tanks. Once the tank is more established with plants they will outcompete it.