It depends on what you mean by split fins...
In some cases of Fin Rot, fins can split... other cases of split fin can be caused by injury (attacked by another fish, handled roughly when trapped in a net, like by the pet store when they are trying to catch it)... poor water quality is also a culprit
I guess there are a few things you need to tell everyone...
is this a new fish, when did the splitting occur (when you got him home, over time, a while back, recently,) is the only symptom that the fins are split, what is your water quality like.. (Check your nitrates, nitrites, ammonias), do you have other more aggressive fish in the tank... how many fish have split fins... if you can snap a pic, that's helpful too.
Different causes will be treated in different ways... so the above information is needed to really help out. I'm no fish expert, but there are a lot of them here, and they'll probably ask for more info.