Maximizing pressurized filters efficiency?

Hi, folks.

Our pond is rather small at only 280 gallons. After a few years of using an
inpond integrated pump/homemade filter (lava rock, scrubbies, etc.) last
season I ran across a good deal on a Hozelock Bioforce 500 UV filter and
Titan 550 pump. It has worked fine over this past season but with a new
hatch of goldie babies, I'm finding that the filter foams now need to be
cleaned every other day - - which is a pain in itself, but even more so as
this unit does not feature a backwash.

Without having to spring for yet another filter system, I would like your
thoughts on how I can:

a) augment the current Bioforce filter ..how can I improve it's efficiency,
or add more filtration? Has anyone tried adding BioBalls to the bottom of
the filter cannister, below the 2 foams? ..or perhaps adding back the old
inpond filter setup?

b) stop the females from constantly producing, etc. In other words control
the population (currently at 30 with (8) 5-6" goldies, comets and
skubunkens).

It's early in the season and the water is still clear. There are already
several plants in place and the pond is sunny about 5 hours/day in the
summer. We are on the Pacific West Coast.

Thanks. Jack