Dunno. 4000 square inches wouldn't be that hard to do. Hardest part would be the amount of light you'd need. For size reference, a 4x8 sheet is 4600 square inches. You could run 2, 2' tall by 8' long screens down behind your 18 foot tank, with 8 foot fluorescents for lighting. Be a neat project. I'd wait for someone to weigh in on it's freshwater effectiveness before putting all your eggs in that basket tho