It is a PITA to clean an UGF
. The classic way is to tear the tank down, remove the plates & scrub it. You need to do that once every year or 2.
Others have devised ways to get around it - some have siphon vac under the plates using airline tubing, but the best I heard of is using a length of 1/2" tubing attached to a shop-vac. If you kept up with the vacuuming, you can avoid the tear down for a long time.
, the UGF
is only good if you run it with powerheads, and best in reversed orientation. <Ie - water is sucked in the up tube & pushing out of the gravel.> In a planted tank, it is a problem. If you have any rooted plants, the roots will get into the slots & clog the plates. Plus, it is even more of a PITA to do a tank teardown with plants....