I remember a thread once regarding this. I have stock fin unused because it doesn't have any bite. Seems to be sliding all over the place. Nice outline slalom fin . Just saw it this morning under a pile of old ones. It's G10 and very smooth like marble. Should the surface be a bit rough like the better fins and what I have tried? If so how do you sand it and what grit sand paper? It's a Kinetic 34cm and 38. They just seem so unusually smooth than most fins I've tried. That's why I really don't bother using them unless they are meant not to be.

in the 80's apparently people wet sanded their fins and bottoms {of their boards that is}
now i noticed the Makani fins had a VERY smooth finish compared to my Select fins and i asked them about it

this is what Louis {founder of Makani} had to say:

"The wax effect will disappear after certain use of the fin, what it is important is the finish with the grinding paper. The Hahalua that you have has been finished with a grinding paper 1000. You can optimize the frictional resistance by grinding your fin with water grinding paper 400 to 1000. The difference between 400 and 1000 is really minor comparing to the resistance made by the cross section of the fin (foil). Let say quickly that a 1000 grinding fin will have less frictional resistance, better lift but a bigger spinout sensation when it happens by going upwind. The 400 finish will give a less spinout sensation but more frictional resistance on the water flow. "

Interesting ..the thread I remembered didn't mention effects of various grit's. Maybe I'll start with what I have currently around the house 250 : am wondering though if the leading edge should be included but keeping the same outline and not doing anything drastic. I gave 2 powerbox fins to a friend for use and everytime I mention what the better ones in the lot were, certainly it'd be always rough

250 will be a bit too rough I reckon. Start with 600 to 1000 wet.
I see what they say about it not making much difference (miniscule scratches from paper vs the foil pushing thru water) and that makes sense......but I think 250 has too much chance of knocking of leading edge radius and nice sharp tip edge

thanks for the advice .. but how do you sand from leading to edge back and forth?