Berlin Systems

In a marine set-up you want to avoid changing things and this means avoiding changing as much water as possible. The nitrates that conventional filters leave behind can be dealt with by

The Berlin system uses a protein skimmer, a mechanical filter, lots of water movement and 'live' rock.

The mechanical filter is just that. Its job is to get rid of solid wastes from the tank. A powerful external filter does the job well and has the added bonus of producing lots of water movement. Something that turns over the tank volume two to three times an hour should do the trick. This filter must be kept purely mechanical i.e. the media should be replaced or cleaned in tap water to kill any bacteria at least once a week. This is essential to keep the nitrogen cycle (biological filtration) in balance.

The biological filter takes the form of live rock. This porous rock comes complete with a population of bacteria, sponges and tube worms all of which help to clean and filter the water. The bacteria in particular form a balanced community of bugs that will convert ammonia to nitrite, nitrite to nitrate AND, in the oxygen starved interior of the rock further bacteria convert the nitrates to oxygen and free nitrogen gas. It is because this is a balanced community relying on the percolation of water through porous rock that we must restrict the amount of biological activity produced elsewhere. If your mechanical filter becomes 'live' it will produce extra nitrate which the rock will not be able to cope with. The tank water obviously needs to be in contact with the rock and this is the reason you need lots of water movement, from your power filter but also some additional pumps or powerheads.

This system has a lower stocking level for fish than a fish only system but you can keep corals and other invertebrates in this kind of tank. Fish obviously need to be 'reef friendly' so large angel fish and Triggers, which eat corals and live rock are a no-no.

Lighting is important. It needs to be reasonable but not very intense unless you want to keep light sensitive invertebrates like some anemones and corals. About 30-40 watts of florescent light/ square foot will normally suffice. This should consist of a mixture of bright white and actinic blue lamps. Alternatively metal halide or the new LED lighting is suspended over an open tank provides intense sunlight effects. Intense lighting will enable you to keep hard as well as soft corals.

You can get away with fewer water changes ( 20%/month ) but you will need to top up evaporated water using pure water. You will also need to add supplements and trace elements like Strontium and Molybdenum, Calcium and Iodine on a regular basis as they are used up by the coralline algae and corals.