Would it be possible to create a self-sustaining ecosystem large enough that could support a complete food chain long enough to keep a pair of medium sized large egged octopus(more then likely O. Briareus) through two complete life cycles? It would be a closed system with no sump. Water movement would be from large pumps beneath rock piles pressed against the walls/corners for water movement. Various macro algaes would litter a deep sand bed to aid in water purification, oxygenation, and removale of phosphates and nitrates. The rocks and algae will be there also as refuge for various animals in the food chain to gain shelter from predators and aid in reproduction. The tank will be void of any organisms capable of stinging, fish, or any large apex predators that could harm the octopus or damage their food supply. It will be completely an invertebrate only ecosystem. The entire system will be light by metal halides hung above. Water treatments(i.e. Ca+, trace elements, et cetra) will be given as needed.