For the fin curling: Try getting some clean driftwood (Petsmart sells some with fake plants attached). It'll soften the water a bit and might even revers some of the curling that he's got from being in hard water. I've got three crowntails right now to I have to look into buying some if I want their fins to be straight. It isn't needed though since it doesn't really harm them at all.
For the filter current: If you can get a hold of an aquarium sponge or two you can baffle your filter by putting it on the intake of the filter, which slows down how much water it takes in at a time, and stuff the other one where the filtered water comes out, which helps to soften the current. Another method is to takea water bottle and make a baffle out of that.
Here's a guide on how to do it: