there are so many ways to offset the increase flow rate:
increasing the volume of the filtering media constrict the
flow of water, thus, you increase the collection of particles,
and reduce the discharge rippling. to much current is dangerous
to fishes too. (as you have mentioned, ripped-off fins)
most of the time, pond pump is just simple submersible pump, attach to
a DIY filtering system like a swimming pool filter... they work effectively
at low wattage. if you can get a picture of simple schematic layout for it,
i can be at your service for evaluation, free of charge...