The dream tank i plan to build some time in the future is a Orinoco river biotope tank in a very long and wide tank. Ideally this tank will be 20 feet long by 4 feet wide (though obviously the eventual size really depends on how large the fish house i can build is) and will be set up in such a way that the water enters at one end of the tank and leaves by the other for the filtration so as to create a naturally flowing tank. I will set the tank up with 3 zones to offer different habitats for the fish to choose from, the first will be a rocky zone with large rocks piled up past the water line, this will be the end the water enters at and will recreate a waterfall habitat for plecs and other fish that like a fast current. The second zone will be a bare sand area for fish that preffer a clear area such as stingrays and eartheater Cichlids and will cover approximately half of the tanks total area (10 feet). The third zone will be a sunken forest area with tall pieces of driftwood and lengths of mangrove root use to reprisent broken tree roots and fallen branches for fish which like to lurk and hunt in areas like this.
This tank will never need any water changes as i will set up a 100gpd R/O unit above it which will constantly drip fresh pure water into the tank and the excess water will leave via a overflow in the filtration system.