Do nipped fins grow back?

Yes (at least in FW), but it usually takes a few weeks depending on the severity of the damage. I've had good luck with Melafix to help heal faster and protect from infections and fungus.
 
Have you witnessed the fish being nipped? Fin erosion is often the result of water quality issues rather than from being nipped. Testing water parameters might be indicative.

The fin may regrow, if it is from being nipped and you can stop the nipping. If you can't, the harrased fish isn't likely to make it.
 
nipped fins

great, I hope they do grow back because the sweetlips are beutifull and my little clown has been taking them both on, ive now removed the clown, he now takes residence in the bathroom toilet.. just kidding, hes in my hospital tank untill i can find him a new home..
 
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