I really dont think this would be that hard- although it would be expensive. With a tank this size (Im thinking 7,000-10,000 gallons) you would want to power it yourself i.e. solar generators and wind power. Picture this- a greenhouse (totally enclosed) with a big pool in the middle of it. The pool of course is the salt water reef pond. Outside the greenhouse are solar sheets which generate the power to operate the pumps, etc. If needed, extra power could be generated via wind. Electric bills would make the salt water reef pond impractical (this of course eliminates that factor) Depending on where you live you would need lights--but if you live somewhere like FL, CA, etc. you wouldnt. If you think a little bit out side the box this doesnt seem so far fetched. Imagine snorkeling in your own reef!
When I get rich Im gonna build this thing...and you guys are all invited as long as you arent weirdos,