well, I went a slightly different route and am glad I did. I started out with ONLY a bog, thinking it would do dual service as both biological and mechanical filter. When I HAD to clean the bog, I knew something else was necessary so I investigated the different types of mechanical filtering (the bog is more than an adequate bio filter). What I ended up doing is something aquarists use, but on a much larger scale. I ended up using 'sump' filtration', by which I mean the water is dumped into a 'sack/bag' filter and then given to the bog for further polishing. The idea was to create a larger filter surface area so I didn't have to clean it all the time. I like low maintenance. I set this up in late February of this year and never had to 'clean' it, not even once. My filter surface area is about 1400 sq in and CAN be cleaned, if I choose/need to. What it is is a piece of filter material (polyfil sheeting material, something you'd get at a craft/material outlet--but it should be eco friendly so as to avoid any flame retardants being added) held in place with a rigid plastic 'cage', mainly for vertical support. The water is dumped into this 'large sack' and as the filter material fills with particulate, the water level rises and uses a 'clean' portion' until finally, the whole 'sack' is clogged. Then, either I yank it out and hose it clean or, as in my case, just replace the filter material (cost me $12 per 5'x2' piece). I anticipated cleaning maybe twice but every time I checked, the level stayed below the top and so, I got a whole season without any maintenance at all. I'll get another filter material piece in the spring and re-load the filter.
This whole filter is housed INSIDE a 55 gallon barrel with appropriate inlet (at top) and outlet (at bottom, so I get a gravity fed-to-the-bog system) plus an additional outlet that goes directly back to the pond. All inlet+outlets have valves so I can control traffic however I wish. This is a bit of DIY but totally worth it. No more bog clog and a mechanical filter that also acts as a settling chamber (as the filter clogs, the water rises and any larger particulate never reaches the higher 'flow-through' portion of the filter. Plus, I have my inlets set about 1/3 the distance from the bottom so water HAS to dwell in the barrel's bottom for a bit.)
I'd recommend this for anyone who doesn't want to put a lot of time and money into filtering their pond mechanically. And since I used a plastic mesh cage, there's also more bio action, beside what the bog offers). I think my total cost including pipe parts and tubing was in the $150 range (I used 1-1/2" overall), and that would have been less if I'd gone for a used barrel without a screw-top. I camouflaged my barrel as it was a retro-fit, but placement means a very easy 'clean' if I ever DO need to hose the filter down mid-season.
Just how I did it. There's a thread with my questions and designs, if you're interested and want to search.
Michael
