I have the opportunity to purchase a TetraPond UV-1 clarifier for 30 bucks;
but the question at hand is weather or not I would be able to use it with my
current filter setup.

My current setup consists of a Beckett BioMechanical filter box with a
325gph pump inside with ammo rocks and a prefilter with a carbon pad as
well. This is being used in a 300 gallon Rubbermaid stock tank. Housing two
Koi and a Comet. They seem to enjoy each others company and hang out
alot....

Now how would I go about hooking one of these up? (That is if I even CAN use
it). The clarifier in question is not submersible and I must keep it outside
the pond. But I think that's gonna throw me a curveball as far as my filter
box is concerned. So what do the experts think? I am at a loss. I guess I
am going to start pricing a tetra filter just in case my idea is no good!!

Any help would be appreciated and my fish will thank you all for it!!