BEFORE making any decision. I would first look at several ponds he has installed.
Since the consultant made reference to bottom drains and no rock bottom pond, then this gives me the impression that he knows something about
understanding currents within a pond to obtain a self cleaning pond. Essentially, you want to make your pond into one big toilet so that there is very little settled debris.
If you're dead set on the bead filter, then look at how the
Ultima II bead filter and the
Advantage bead filter are constructed and take notice of the extra functions they perform. These are the two most highly recommended bead filters have I read about on koi pond forums. Personally, I would rather use
shower tower bio-filter or a
moving fluidized bed bio-filter (and
here's a kit you can buy to help you build it), but you really need to have the water mechanically filtered before entering these bio-filters; this is kind of where bead filters is different from other bio-filters. It is easier to flush out the debris in a bead filter, but this is not necessarily a good thing to be distrubing the bacteria like this all the time, except it has to be done with bead filters. The better mechanical filtration will reduce the frequency of bead filter flushes. Eventually, I find folk using their bead filters as a mechanical polishing filter and then using a different bio-filter. Generally, I read folk selecting one or two sizes bigger than your fish stock density when choosing a bead filter. Personally, I really do not care for bead filters, but I guess my opinion would change if I saw one in person operate in a high stock density pond, although I doubt it could prove me wrong; I just don't have much faith in them. I put bio-filters into a ranking and bead filters would be #3 just below moving fluidized bed (#2) and below a shower tower (#1).
If you want your bio-filtration to perform the best it can, then you will need to mechanically pre-filter the water before the pump that is then pumped into a filter that polishes the water before it enters the bio-filtration. This is how a pond's filtration system can get expensive. There are many many options for mechanical pre-filters and mechanical polish filters. Personally, I think the bio-filtration unit should be the cheapest unit of the entire filtration system. Here's
an example video of a very good pond filtration system that is all DIY'd. Of course, the DIY type of approach tends to require more of an area footprint, but it is all DIY stuff so a bit cheaper than buying it retail. If you want to go the retail route, then here's
an example video of a very good pond filtration system that is craftsman made. This retail appraoch is a bit more expensive, but the plumbing can be changed so the mechanical filters and pump only consuming a 28" by 31" area foot print. Personally, if you got the money for the retail option, then I would lookup
Deepwater Koi and
here's a thread talking more about his products.
There are many many options you can choose for mechanically and biologically filtering your water, but I suppose just a bead filter is a good beginner filter.
Also, it is often recommended by koi pond hobbyiests that bead filters needs water that is near 200ppm KH or higher for it to perform the best it can.
