Question Please Help Me!!!!!

If I have a power filer do i need a undergravel filer

 

Well you haven't told us anything about your tank, but for starters...no.
Undergravel filters are not very highly regarded by many, and not necessary. A hang on the back filter or a canister filter will do the job very well. The main reason people do not care for undergravel is because of the high amount of debris that collects under the plates. It makes the job of cleaning a tank much more difficult!