Welcome to the forum! It's definitely freshwater slime mold in my opinion. Googling it will have a bunch of management advice. You can just suck it out of the tank when you're doing a water change. It could have formed if you're overfeeding, not doing enough water changes, or have an improper amount of lighting in the tank. I'd bet it's the former two, but don't really know. I agree with pheonixkingZ about what your course of action should be. Maybe get some super easy live plants while you're at it to help suck up the ammonia.Hello,
Do you know what happening in my guppy tanks? Pictures included.