my turning fin

[Why Not]

My fin is getting chewed up from something, I toke a file and smoothed the cutting edge and had a nice smooth sharp tip and now after a couple of rides its all rough, and its like its been hitting something. The lake is super clean had no sticks nor do i think they could do this to it, and its never gets close to shore unless it being taken out but when that happens we fold the fin in. Any help is appreciated.
Edward

[Dave S]

Finmites...........

[rgsauger]

The front edge should be filed to a radius or somewhat round. The trailing edge is the one that is often sharp. How fast are you running?