Gravel Cleaning and Filtering

I've got the Pond Fish in a 65 gallon tank for the winter, so I'm a little
new to the aquarium cleaning.
I'm using an AquaClear 800 and two Penguins for the RUGF. All intakes are
pre-filtered.

I've been using a Python to clean the gravel every two weeks. I stop when
I've removed about 30% of the water, but the gravel is still not as clean as
I'd like. There still seems to be a lot of fine crap in the water after
cleaning. The existing filter does nothing to trap this, but it does
eventually settle out of course. I suspect this is extra food, as the fish
seem quite busy chasing this stuff.

So is there a better method for cleaning the gravel? Will a change to a
canister filter remove more of the fine crap?