It will be a lot, as you face several issues. First issue: This is a very large pond you are looking at, in the range of 11,000 gallons (using the calculations you provided). It sounds as if someone had a very serious koi pond at one time. Although you state you are leaning toward not keeping fish, I would want bottom drains installed in a pond of this size, or you will end up with a mucky mess in a couple of years. If this was a properly designed koi pond, some of that plumbing may still be in place. So the first consideration is that you will need a pump that will filter something on the order of 5,500 to 10,000 gallons per hour, 24 hours a day. A Dolphin Ampmaster ES5500 external pump would perform this function relatively inexpensively, at about 286 watts per hour. I've seen that pump listed for around $400. The second issue is that a pump like the Dolphin will not push water to the heights you are considering for your waterfall. You need a pump that will push 40 feet or greater "well head" height -- the vertical distance that a pump will raise a column of water. For this, you will need a powerful unit like a Sequence Primer which draws around 1500 watts per hour. That is about the same as a large window air conditioner. Where I live in Virginia, the math works out like this: 1500 watts = 1.5 kWh x 7 cents = $1.05 per hour. (I think the national average cost is more like 10 cents per kWh.) Therefore, since you must run filtration 24 hours a day, you are probably looking at two pump systems. The filtration could be accomplished with a low-cost unit like the Dolphin. Your waterfall would be fed by a second very powerful pump that you'd run only for those hours each day when you want to operate the waterfall. You could reduce your cost somewhat by lowering the height of the waterfall. If you are serious about this project, I would recommend first reading up on koi pond design and construction. (There are several websites which specialize in this subject.) Also, some of the experts around here will hopefully chime in. This is not a "garden-variety" pond project that you are considering!

Hi all - wow thank you for the input! For some reason a few of these comments never made it to me via email, so sorry for the delay in response. CHAS: I think I'm going to just go with a shorter stream, which will cut down on the height a great deal. I will wrap it around the pond (instead of going straight up the sloped ground) - which will make the head height less and also keep the flow calmer for froggies. I also decided that I will focus the main pond on fish; and I'm going to put a little, shallower pond tucked along the creek which will be just for frogs - with a pump maybe, but no filter or anything (my current frog pond has just a pump/waterfall, no filter, and the frogs are very happy and healthy there). Hopefully the frogs will natuarlly choose the little pond instead of the bigger pond, and even if they lay eggs in the lower pond, I can just move them up to the froggie pond. I at least will feel like I've done my part to provide a safe haven for them :) RSINGLEY: I had read a similar recommendation elsewhere of putting mesh and other media around the pump - I like the idea, though I do wonder what the negative effect of not filtering the larger particles will be? (seems silly to get a debris handling pump and then restrict the debris from getting in, but alas, the dilemma of tadpole lovers). FROGMAN4: You'd be right on the calculation but it's not all at a 3.5' depth, and it's an oval pond. If you picture an upside down oval wedding cake: the biggest layer is 16x13 but it's only about a half-foot deep (it's a rock shelf). The second layer is 14x11 and is 1 foot deep. The third layer is 11x8 and is 2 feet deep (so total depth at the bottom will be 3.5). I calculated each "layer" out as separate pond volumes; using the oval pond forumla of L x W x D x 6.7, the top layer is 696 gallons, 2nd layer is 1031, 3rd layer is 1179 = 2906 gallons. The third (bottom) layer will have sloped walls, too, which actually will cut down the gallons, but I'm fine with over-estimating. I have wavered back and forth a hundred times about going with a skimmer filter as opposed to an external mechanical filter. I still haven't hit the "place order" button on my pump/filter order, but I made up my mind last night that I was going to go with a Laguna max flow pump (2000 gal), pressurized filter (3200), and also have a waterfall bio filter at the top. Holding off on the drain for now, but I saw some that I can add later if the need warrants. Chose the external filter instead of skimmer because I didn't want to have to do 2 pumps, and I just felt that not having the pump at the bottom (which it wouldn't be if I put the pump in the skimmer) wasn't the best idea... which was my deciding factor. I hope what I'm choosing will be sufficient... weeks of research got me here, and I'm ready to just install all this already! :) MEGANMCA: Thanks for that link - it's very helpful! I did read that pipe diameter is important - I'm going to go with 1.5" and hope that's sufficient. My sister just installed the same pump/filter combo I'm using with 1.5" and it's a beatuful flow. Her waterfall is a little lower than mine, but I think it will suffice... If not, can add a 2nd pump but hoping I don't have to do that. Thank you all so much for the input - and as always open to any other thoughts/suggestions!

I think your first idea was better. For low maintenance a bog is very good. Pitch the filter entirely. I've built many filters....many. What I learned is people way over think them and make them way more complicated than they need to be.

What size pool? 400' of decking? Are you only going part of the way around? If there is no spa, and this pool is the size I suspect roughly, a 2 HP pump is way too big. I do like the big cartridge filter though. Less cleaning. Intellibrites are very worthy of your considerations. Ask for a three way valve at the pump exhaust. This will allow you to vacuum to waste. Otherwise I foresee a hose bib that is only useful for lowering the pool's water level after a rain. Specify schedule 40 pressure rated pipe, no flex. Check for rock at excavation in the contract. Scott