usually those tanks are designed with keeping betta fish so they can be slower in power. If its the one I'm thinking, it comes as a whole unit with the tank so there isn't much to be done in terms of power. at most the best I could say is try running it without the filter media to see how fast it should be pumping out water without any barriers, or if its barely pumping water water there might be something wrong with the motor(clogged or defective) but as I stated before they are designed with low flow in mind. If pollution is what you are worried about throwing some live plants will help. I think I have seen people put certain house plants in the filter itself. Good luck though.
I took out the filter media that’s suppose to go in there and cut out to fit my own with floss. I also put bio stones in the top whet water runs down. I do have a Betta in there. I also put plants in there. I can’t think of anything else to do.