I agree that replacement might be the best option. We use & sell those in the store I work in, and they're pretty much garbage. The pump inside it is 80 gph, and you can't control it. However, they do clog pretty fast, so once it's running for a little while, you'll have the exact opposite problem- not enough flow!
The only thing I can think of to slow it down is if you were to go buy a sheet of filter fiber, or quilt batting, cut a strip out of it, and tie it around the base of the filter where the water intake is. That might help a little.