What is most likely happening is there is a short somewhere in the pump, the amount of current going in is not the same amount coming out and that is what's causing the gfci to trip.
Trying to repair the pump might be possible if it is just a loose wire but if you open the housing you might not be able to reseal it properly and that could cause much bigger problems.
To be on the safe side I would replace it.
How old is the pump? Is it still under warranty?
Also do you have magnetic or electronic ballasts? I've read that electronic ballasts can cause problems with gfci.
http://www.sylvania.com/forum/pdfs/faq0011-0297.pdf
HTH S.C.