Filter Size??

Hi, was wondering if someone could tell me if I did the right thing here. I
built a Biofilter for my pond.It is 12X7X2. The one I built is 9gal.
basically a square Rubbermaid box. The pump (1200gph) pumps into the "top"
of box through an 18W UV light, then goes into filter through a 1 1/4" thick
Med. filter pad. It works its way down through the filter media. The media
is a combination of Bio Ceramic Barrels,Two bags of Lava Rocks crushed into
smaller sizes and regular Supra media, then finally exits out the bottom
into pond. Will this design keep water ok? Thanks..............