Bad pump or filters?

We have a pondmaster pump/filtration system. I believe this is what we have
can't remember http://www.pondliner.com/PMK1500.htm. We use it only in the
winter, we run our 14ft. waterfall and larger filter during the summer. Last
winter was our first winter using the pump. It would run a month or longer
before the filter pads needed cleaning. We would pull the pump out for
cleaning when the fountian spray dropped down to the ponds water level. This
year the fountain spray drops within hours of cleaning the filter pads! So
we got new filter pads. Our fountain spray was high like it should be with
the new pads for about 3 days than it dropped like a rock. We pulled the
pump/filter out to clean the pads today about 3 hours ago and already the
fountain spray is almost down to the pond surface.
Are we dealing with a pump going bad? If it is going bad why did the
fountain spray stay high for 3 days (after getting the new pads) before
losing it's strength? My thinking is if the pump was going bad than the
fountain spray would not have stayed up and would have dropped within hours
just like before the new pads.
Any ideas?