oh it will be the male guppies being really nasty and they will rite and it is nasty if they become allbrown around the fins just tell us because then that is bad but the nips will always be there unfortunatly.
thanks
Mat
As long as youre sure they are just bitten and its not a rot then clean water will be the best thing and maybe a touch of melafix to stop any infection.
Try adding some melafix. Are they alone now? Male guppies should be in groups of at least 5 to spead out the agression, and should never be kept with nippy fish as their fins are very inviting to them.