I'm told just takes a bog the size of a couple whiskey barrels to make crystal clean water for a few thousand gallons of pond water. Don't know what size, 40gal, 50gal, 66gal, 130gal, whiskey barrels come in all sorts of sizes.
Too many bog owners act like a bog is the final answer to it all yet they say its not even though they act like it is. Quick bit of sarcasm, "yeah, i got perfect water, no algae, and all I use is a bog so it must be the bog and can't explain why it works so good and all I have are plants so it must be the plants also, but its not the final answer even though it is the final answer for me and it could be the final answer for you" Giving me the impression that i'm silly for not trying a bog and it is kind of the same way with skippy followers. The circular discussion drives me crazy; it kind of feels like talking to my mom when I am asked 30 questions before we actually start having a conservation. Drives me crazy!!
Only reason why I use these other mechanisms is ... all together, my little skippy (did it mainly cause it is multipurpose creates a good waterfal and does some bio-filtration), trickle tower water fountain, dinky pressure filter, would fit in a 2'x3'x1' rectangle with all the plumbing going underground and the outflow creating aesthetically pleasing waterfalls. I bet I could replace/improve these mechanisms further and seriously push the fish volume limitations of my water's ecosystem such as having a nice little bunch of Rosey Reds with a good handful of shunbunkins and other comets in just 435 gallons of water.
Aquariums you often see in restaurants and hotels are seriously overstock. This is only possible due to their fancy mechanisms. It would be very interesting to see how well a bog would work for the overstock aquarium's without additional mechanisms.
Fact is we're talking about very hardy goldfish that often live in stagnant muddy water. It doesn't take much if ya are not seriously overstocking your water ecosystem.