For filtration, if you decide to go with the 10 ft dia. pond, id reccomend a 4" bottom drain, plumbed to a 200+ gal. settling chamber, then have the output pipe from the settling chamber go into a fluidized bed filter, filled with kaldness k1, a 9" air diffuser mounted on the bottom of the barrel to provide air, id go with a medo 45b airpump hooked up to the diffuser, then from the fluidized bed, have it go to a sand/gravel filter ( 55 gal drum also) then have an es3500 return the water to the pond, via TPR's or something else. but mainly the filtration depends on how heavily the pond is stocked. if you have any questions feel free to PM me or post here.