I have had an experimental 70 gal tank set up for about 2 months. There are no fish in this tank but it is gravity feed from my 210. The set up has a 7 inch dsb. It is split down the center length wise. Think race track and you will have the idea. One half of the tank has ruble from 1-5 inch with various types of algae. The other side is coral frags birds nest, acro, Zoas, chalice, mushrooms, blasto sponges, fan worms and rock anemones. 1 600 gph pump pushes water in the same direction as the gravity feed. Tho causes the water to follow the race track. A phosban 150 with 2 Tbsp of Bp. The Bp are to increase the free bacteria available as a food source. The exit also flows in the same direction. It has 1 t247 led light on the coral side running at 20% on the blue spectrum 7 hrs and 10% full spectrum 4 hrs, and a PC on the other 10 hrs. In 2 months it is loaded with life 1000s of mysids, amphipods', copepods', worms, starfish. The water circulates around the top fairly quickly but the bottom 1-2 inches moves much slower. The bottom 2 inches contains 90-95% of the life. The coral are multiplying faster than I have ever seen in my 12 years of reefing. The lighting is turned way down and to my surprise the colors are better than ever. I have ran a refugia on the 210 for 8 years and there is way more life in this setup than the 8 year old setup. Both setups are connected to the 210. The starting culture was rock and algae taken from the 8 year old setup. Additives bacteria 1 tbsp every 2 weeks, reef bugs 2x per week 1/16tsp, vodka .5ml 1x per week. These are added to the 210 display. These are all to increase the free bacteria count. If I turn the pumps off you can see plankton swimming to feed on the reef bugs. The display has 1 very fat mandarin and a leopard wrasse along with 2 clowns flame angel, gobies', tangs, shrimp, starfish, yellow tail damsel. The older system is also a 70 gal it has 2 inches of mud same algae, rock, same PC light, no led no direct Bp feed. Gravity feed in one side out the other.