I moved into a house that has an existing pond that was never finished. Not taking into account all the plumbing that comes with proper filtration, the builder concreted a larger square pit next to the house then never completed the project. Iím guessing it to be approx 1500 gallons. Because the concrete is already poured, I canít retro in a bottom drain. Definitely canít dig up the concrete since it would break the driveway and part of the patio. Because of the location in the yard, I canít dig a filter pit for a gravity fed/external pump filtration system. I am reluctantly realizing the only way to turn this into a koi pond may be to use a submersible pump with the output going to an above ground filter system of some sort. Iím wondering if I use a submersible pump, would a diy vortex settling chamber made with a 55 gal drum be useless in conjunction with any reasonable flow rate as the pump would churn all the waste solids smaller and into suspension? The area where the filtration system will be only has enough footprint room for about two 55 gal drums. Iím trying to make the most of existing situation and area that I have to work within. Any ideas for filtration in conjunction with a submersible pump would be greatly appreciated.