Question about water fountain water bowl.

I got my cat one of those water fountain drinking bows as per the suggestion from the breeder but I've been having a significant issue with it, and that issue is.... Mold.... I think? Idk, I change the water like once a week, the instructions say every 2 WEEKS but even when I do it in half that time the water reservoir part is just filled with grey slime looking stuff, its floating in the water, its all over the filter part that leads up to the fountain and basically just everywhere inside the thing. I don't want to have to change the water in it every day which is seeming like I would have to do to combat this so I'm thinking I might just go back with a regular water thing. She drinks out of the 2 dogs water bowls all the time anyways. But, has anyone else had any kind of issues with these things like this?

PS: I always fill it with filtered water from the fridge but that doesn't make a difference.