you can get help at koipen.com and they have lots things about filters on there to hope this help ho more filter than you think i would say 250 gal.but that will take care of a lot of fish need more info like pump size ,how deep pond is ,over all size of it .

well the pond is going to be around 3 feet deep and i think like 10 foot long and 5 or 6 feet wide. there will be a bottom drain in the middle deepest part of the pond and also our pump will be in a diy prefilter/mechanical filter. we have two lily pad plants that kept the water about half covered last summer and also we will have some floating plants that i was planning on putting in the top of biofilter if we used flower pots(to hide the filter a little more) as far as the pump goes i am unsure what the flow rate is. we bought it two years ago and it was running our waterfall quite well. i guess at those calculations our pond would only have about 800-1000 gallons of water. thanks for the help and i cant wait to hear more

my pump is a 1200 gallon per hour

Just wanted to let pond builders know that Lorentz.de makes a solar pump that works really well for koi ponds. The pumps are 92% efficient compared to most other pumps that run at 45% efficient. They can also be supplimented with a/c back up if they wish to run 24 hours a day and will still be running a very efficient pump which will cost them much less than a conventional pump. Here in Hawaii this system also qualifies for state and federal tax breaks which is always nice. That's 65%! Not bad. I deal these pumps whcih come with a full 5 year warranty also. This is groing rapidly popular here and I am sure it will elsewhere.

Think BOG FILTER! I dug a hole two feet deep in the ground, then built the sides up above ground with toung and groove car decking bolted to four fence posts set in the earth to get a four foot deep pond that is six feet wide, 8 feet long, and four feet deep. I put in a heavy duty rubber pond liner (feels like inner tube stuff). Outside of this pond I built a plywood box four feet wide, eight feet long, and 1 foot deep This is sitting right against the pond wall, tilted up a bit in the back to aid gravity flow of water into the pond. This has its own piece of rubber liner which flops over the front edge of the plywood box and into the pond. I filled this box with pea gravel. This pea gravel is planted with water loving plants. I have about 1000 gallons in the pond, and the bog filter holds about 100 gallons and recieves its water from a 3500 gallon per hour pump with a 2" pickup hose in the pond, and a 2" hose delivering the water to a 2" spray bar at the top side of the bog filter. All plumbing is 2" pvc. I laid a fence board over this pipe to keep it from showing and to keep the water going into the gravel instead of the air. I'm going to make the outlet holes in the pipe a little bigger so the water can flow out rather than be ejected under pressure. Fish water thus runs through the pea gravel and the plant roots suck up the water soluble nutrients and clean, aerated water runs back into the pond. There are 18 goldfish in the pond who are healthier than I am. The box shape of the filter is softened by the iris and some other low growing plants that have practically covered the gravel. The pump is super quiet and sitting on a table at the far end of the pool. We have a tiny little brick patio opposite the end with the pump where we like to sit and watch the fish. We have all kinds of plants growing around this installation and we never notice its shape anymore. By the way, the box with the pea gravel bog filter in it is sitting on top of dry stacked cinder block piers to bring it up to the edge of the pond. Support the filter box well, that gravel and water is heavy. You don't need to make a box, you can do yours in the ground near your pond. Let it be known: I do not like canister filters, pumps that are too small for the job, mechanical filters whether they are ugly or not, and cleaning said filters. These things wear out over time (like everything else) and eventually need to be replaced. My pond/bog filter/pump combination is two years old. We had an algae bloom for three months at the very beginning before the plants in the filter had become established. Now the water is clear all the time because the plants eat all the nitrites/nitrates the algae need to flourish. Figure your filter capacity based on the volume of your pond, not its surface area. Give the filter extra capacity by making it bigger than ten percent of your pond volume. The best thing about a bog filter is that you never need to clean it and you can have your pond surrounded by beautiful plantings. I am currently trying to figure out how to do a bog filter for our tropical fish indoors. If I can do this hat trick I will probably never use another canister filter as long as I live. I know, this is a book, but do your research on bog filters. Call some commercial water plant growers and see if they have ideas you could use. Read, read, read, and then try something. Have fun!