Very interesting thread. I found it while doing some research on a 10' (small by comparison!) salt water tank setup. One interesting point about the tank I'm planning is that the lighting will come in thru the roof via 2 sky light type penetrations (glass globe on top, with a silver tube running down). The roof will be concrete but will have a latex membrane sandwiched in between two concrete layers (makes it waterproof).
A couple thoughts about heating, filtration, etc:
Heating: you can get 500 feet of thin wall black tubing (used for wells) for dirt cheap at most plumbing supply places. The thin wall helps solar radiation heat the water inside. You can use a very slow pump to push the water thru (or just push the water into a holding tank and let it gravity feed). Even dim sunlight with a low flow rating on a cold day would boost the water temperature significantly.
Filtration: bio balls and sand filters are standard stuff. But for really killer water quality, you need to dedicate 50% of your aquarium surface area to holding a "swamp". Basically, you'd be building a terrarium where half of the top was dedicated to plants. This separate area would be filled with sand and a slow flow pump would push aquarium water into it (gravity would push it back). As the water flowed thru the swamp, the trillions of microbes and bacteria would clean the water just as it is done in nature.
Also, by adding "emergent" plants, you are getting natures #1 natural filters as they suck up nitrogenous waste way more efficiently than plants which are fully submerged (because the growing parts are above water, not submerged).
I've done this type of setup for ponds and aquariums (terrariums), and the results are so dramatic (crystal clear water with no other filtration or water movement). Fish load was pretty high in a couple cases (koi being big and messy). Greatly cuts down on the need for water changes too (water quality is Nitrate in less than 1% sustained concentration).
The smallest project I ever did with the above setup was a 10 gallon aquarium (fun!) . The largest was a pond system with a 35x12x2' swamp attached to a 35x10x4' pond. In the big pond, which had 3 dozen koi and 6 dozen+ comets (fed daily), the water was so clear you could read a golf ball (title) sitting at the bottom of the pond.
Obviously such a setup for an aquarium doesn't work if the winter temperatures get low enough to freeze the plants in your swamp.
The other neat thing about this is that the physical separation of the swamp from the aquarium water doesn't need to be "water proof", it just needs to keep the sand out of the aquarium. Also, while you loose surface area, you can actually build a really cool looking overhang, with overhanging plants, just like the really nicely built aquariums (ie the ones people pay money to go see).
Just thought I throw these thoughts out there as I enjoyed reading about your monster tank!
