Bender, I think you have suggested the best option here, as something like this is self-sustaining apart from the smallish water pump to keep things circulating. Those bog plants can remove a LOT of nutrients. The bigger the bog, the better the filter. The drawback is water loss through all of the vegetation, plus bugs if fish cant get in there to keep it cleaned out.

Otherwise our local zoo has several large sand-based canister filters running with at least 3 20HP electric motor pumps to keep up with the seal crap. Those tanks are in the 250M gallon range. Even then it is not pool-clear but not horrible. I think there are some UV sterilizers off of the pumps, but I cant be sure. I cannot imagine the electric costs... not to mention the installation costs.

I say live with a little algae, it is good for you and keeps your immune system working on things it should be rather than attacking silly things like pollen.