Filter Recommendations.

Hi,I am looking for recommendations on external canister filters.
Currently I have a 200 litre tank with fake plants and around 50
fish ranging in size from 2 4 inch clown loaches to a few neon
tetras. I am running a UGF powered by 2 powerheads operating
at a combined 300GPH.The filtration is supplemented by a
Fluval 2plus internal filter. My tank has been running for just over
1 year with no problems. Lately my water has gone from being crystal clear
to slightly cloudy/hazy. I can still see the fish ok,but the hazy water is
annoying me. I'm thinking this is due to a build
up of mulm under the filter plate,so I devised a tube that fits onto my
gravel vacuum that can be inserted under the filter plate.This does remove a
lot of mulm,but obviously does not remove all of it.
I don't want to do a full stripdown of the tank,so I thought I could
improve the filtration by adding an external canister filter.
Your thoughts would be welcome on this.
Thanks.

John.