Hello big tank world, There are 3 Marine Ponds in my outdoor system(s). Each is only 250 operating gallons. The total is over the 400 gallon mark ( 750 gallons ). They do not support Hard Coral because of Phos. levels. What might be of interest is that they support a huge variety of fish and inverts. Two have Breeding Dwarf Seahorse colonies. There are ricordea, gorgonians, mushrooms, and lots of macro algae. The systems that work here can be made from garden center parts. It would be a huge help if someone adapted the system for use with a big tank. I have been posting about dwarf Seahorses in the seahorse/pipefish forum. This system does not require any active coral. All the Bio activity both aerobic ( nitrite ) and anaerobic ( nitrate ) occurs in the twisted weave of Knitted HDPE Shade Cloth. The ribbons of material overlap to form low oxygen areas. A cocoon of Cloth around a pond pump works here. The cloth protects the larva and the pump output is directed for current. It might be that a standard over tank Phos. Reactor could hold enough cloth to do 50 gallons. It is much faster than live rock. The protein Scimmer can be standard or the Gag Hurler used here. These systems in total use less than 300 watts for all filtration. They are outdoors so the color of the water is Planktonated. The filters run for the pump life without cleaning. The Gack Hurler uses one air pump and a valve to go from 0 to 15 gallon of reject a day. Maybe one roll of cloth ( 100 ft by 8 ) in a 50 gallon poly HDPE Barrel and a big pump would process several thousand gallons based on what is here already. The Gack Hurler does an about 50 g/h so it might need upgrading. Someone called my pond a giant Frag Tank. Some stuff likes it. PS: The last picture about Plankton Colored Water had a surprise, there is a Dwarf Seahorse chilling out by the base of a Gorgonian. Sometimes they escape the corral as fry and grow up in the main tank. They get put back in the corral because the main pond is too rough. I have repatriated 6 in the last week.