The Berlin Method of filtration is as follows: Protein Skimmer, a good amount of Live Rock and a Deep Live Sand Bed.
For the Protein Skimmer: a 180 gallon saltwater tank will have different requirements for different setups. Are you interested in a Fish Only With Live Rock (FOWLR) or a full reef? The FOWLR will have different demands based on fish selection, and the reef will have different demands based on coral selection. I think that the AquaC EV 240
would be your best bet for a well-rounded skimmer. This would go inyour sump, so your 180 should be a Reef-Ready tank (holes drilled for overflows).
For the Live Rock: Your tank should be about 2/3 full. It will probably take somewhere around 200 lbs to achieve this. Of that 200 lbs, 150-175 lbs could be dry rock. A lot of members here buy their dry rock at MarcoRocks
. The balance should be Live Rock, bought with good growth on them from your Local Fish Store (LFS).
For the Deep Live Sand Bed: 4-6" of sand. Most of us used CaribSea 20lb bags of Live Sand, but the MarcoRocks site also offers a Base Sand package, and for most of your sand this will be fine. I would use a bag of CaribSea to seed the sand bed with the appropriate lifeforms. The reason that the sand bed is so deep is that 4-6" allows the proper anaerobic bacteria to grow that aids in denitrification. The proccess is as follows: Aerobic bacteria living on the surface of the sand and rock convert ammonia to nitrite and nitrite to nitrate. The anaerobic bacteria living deeper in the rock and under the sand bed convert nitrate to nitrogen gas, shich leaves the system naturally.
These processes coupled with the Protein Skimmer, which removes Dissolved Organic Compounds (DOCs), keeps the nitrates down in the tank.
The last part of the process is the maintaining of Alkalinity and Calcium. The carbonates and bicarbonates that make up saltwater need to maintain balance. We consider an Alkalinity reading of 8-12 dKH and a Calcium reading of 400-450ppm in the normal ranges. Standard practice is to test and dose according to how much your water is "using". I say using because in all reality, corals are using these bicarbonates and carbonates to calcify thier skeletons. Also, as acids are introduced into the system, such as DOCs, the bicarbonates balance the pH, keeping the water more basic.
Hope all this helps! Any ideas of stocking?