Plan is to have bottom drain and skimmer going to a collection box/sediment box then onto a filter. I really like idea of seive but that would cause a break in the chain of suction.
Could pump be a sumbersible pump within the sediment box to help muffle any sound(I assume external pumps are loud no matter how high dollar they are(this will be 15,000 pond so likely a large pump.
Original plan was pressurized bead filter from Sacramento koi following their diagrams as they are compact enough to fit under a porch out of view up on a hill, as I have limited space at the level of my pond to have bulky DIY filters. However I have heard Pressurized bead filters don't get the water real clean and are ridiculously expensive.
Submersible pump can go in the sediment box, and most water gardens do this although owners don't always consider a pond to be a sediment box. If you think about it there is no difference between a sediment box and a pond except size. And the bigger a "box" the lower the water movement and more stuff settles out. For some reason many DIY ponders think if they add a box and call it a "sediment camber" that somehow that's where stuff will settle, but virtually all will settle in the pond. Which is where bottom drains come into play, remove the collected sediment.
I think external pumps are loud, but some people say they aren't. Don't know if it's a hearing problem, background noise or whatever. For a swimming pool no problem, but for a water garden I like peaceful. A large pump is not required for a large pond. Pumps should be sized to water feature aesthetic need, fish load, and devices like some filters, TPRs, etc... There will be a long line of people to tell you pumps are sized to number of gallons in the pond, or surface area, or whatever else they heard last week. That's all has nothing to do with how ponds work and everything to do with the way people work.
You can add my name to the list of people who think bead filters are poor filters. Personally I've not seen any combo filter work very well. When bead filters first came out most people thought they were the cat's meow, me too. They claimed to be a mechanical filter and a bio filter. Over time they've proven to do neither well...or at least there are better options now. Today sieve is top of the line for mechanical imo followed by lots of things, including bead. Almost all bead filters today are only used as mechanical, first in line, filters. But expensive to run for both electric and water used to flush. Sieve costs zero for electric and no water needed for flushing. Bead still have the advantage of being able to be put on timers, pressure sensors, and therefore be automatic cleaners. But normally a sieve can hold weeks worth of debris so you can be away for awhile and not have a problem.
For bio top of the line are Shower and Trickle filters. Proven to be about 10x more efficient for the same size as any submerged media filter. And these filters virtually never have to be cleaned. In addition to less work it means they operate at basically the same efficiency 24/7 while submerged drop efficiency between cleanings and as bacteria recover from being covered in muck. Reliable efficiency is very important for pond that need bio filters. Most water gardens don't need any bio filters at all, the pond itself can handle the load, so efficiency isn't really a factor.
