When establishing a tank, two of the more popular choices are to build a display aquarium or a marine habitat. Each choice has its benefits and drawbacks. They also can have very different needs as to equipment, maintenance, and livestock. A brief description of each type tank and a basic view of their requirements is given below.
The typical display aquarium could be described as a tank setup that has been created with the goal of having an aquarium that provides the most pleasing appearance for the viewer. Usually there is an effort made towards having bright colors from corals and fish and an overall "ultra clean" look to the tank.
A marine habitat is a setup where an attempt is made to mimic an actual ocean reef (or other) habitat. There is usually an emphasis on diversity of lifeforms to be included in the aquarium. The habitat is created with an effort towards making the tank inhabitants feel at home as much as possible.
Display Aquariums
When establishing these types of setups, there are several key decisions that have to be made. In order to have the "eye-popping" colors that many aquarists seek, proper lighting is very important. With T5 lighting, the fixtures usually will have multiple bulbs allowing great versatility in lighting choices. Metal halide lighting will provide great lighting intensity and the shimmer effect that many desire. Your choice of MH bulb will have a huge impact on the brightness of colors in the tank. However, supplemental actinic lighting should also be chosen wisely. With either T5 or MH lighting, it is a good idea to look at other tanks that have the lighting effects you like most, and strive to duplicate that effect by using the same or similar equipment. Power compact (PC) lighting can also be used but seems to no longer be a recommended lighting choice.
Display aquariums also usually strive to have ultra clear water. The clarity of the water aids in light penetration which helps bring out the desired bright colors. There are varying methods used to obtain this ultra clear water. Many choose to create a bare bottom tank. These tanks have no substrate but instead, usually will have the bottom of the tank covered with Starboard (a marine grade polymer). White is the color most often chosen as it helps increase the overall brightness of the tank. A bare bottom tank also allows the aquarist to eliminate build-up of detritus by simply having an efficient flow of water throughout the tank. These type tanks work well for fish only systems with fish that are messy eaters. The lack of substrate makes it easier for the flow to keep detritus suspended in the water column where it can be removed by filtration or skimming. Without a sandbed to get stirred-up, massive amounts of flow can be achieved without upsetting the tank inhabitants. This also creates an ideal environment for many SPS corals that thrive on the high flow.
To further polish the water, micron filtration can beneficial in increasing water clarity. Various other methods can also be employed such as the use of filter socks, canister filters, and even some of the better HOB filters. In conjunction with these filters, the use of carbon and other media such as Purigen or Chemipure can assist in water clarity by absorbing certain impurities from the water. These filter media can also be used separate from a filter system. This would be accomplished by strategically placing the media (which is usually in a filter bag) in an area of the system where water will be forced through the media.
Ozonizers can aid water clarity by breaking down DOC's (dissolved organic compounds) in the water column. An ozonizer will also kill many micro-organisms which will further increase water clarity.
Since these type tanks create a relatively sterile environment, cleanup crews consisting of creatures such as snails and crabs are not as necessary as with other type tank environments.
As in any setup, anemones are only to be considered by those who have studied the specific requirements and possible hazards of owning these animals.
Marine Habitats
Marine habitats will usually attempt to offer a more natural look to the aquarium setting. The idea here is to offer an environment for the livestock where they can feel "at home". Lighting is still an important consideration but with perhaps more of an emphasis on what is best for the tank inhabitants while still considering the aesthetics of the lighting. Often nowadays, lighting systems are designed to simulate a natural daylight cycle. Morning is often simulated by having actinic lighting only. Later, midday lighting is produced by having the MH's or daylight spectrum T5 lamps activated. Evening would again be only actinic lighting.
Nighttime lighting will often have some type of blue lights (usually LED's) used to simulate moonlight and provide minimal night viewing of the tank. Some aquarists even go to the extent of having the entire lighting schedule match actual sunrise/sunset times, and at night to imitate the various phases of the moon.
Various substrates are also used to simulate various environments found around coral reefs. Usually this consists of an aragonite sandbed but may sometimes incorporate crushed coral, liverock rubble, or shells. The substrate is necessary in a marine habitat since there is a great variety of life to be found within the substrate. Deep sandbeds (DSB) are often used since they not only provide a home for the various life found within it, but also for the nitrifying bacteria that can be important for the stability of these type tanks.
Liverock also plays an important part in a Marine Habitat. It provides areas for attaching corals, areas between and holes in the rocks are often homes and safe-havens for fish and other creatures, and it also allows the fish to graze on micro and macrofauna found on the rockwork. Sponges are often encouraged to grow within the rockwork as they assist in filtering the water and perhaps even provide a food source for some tank inhabitants such as linkia stars.
Filtration is an important consideration on these type setups. If the goal is to have a diverse system that includes near microscopic creatures in the water column, then filters must be placed where they won’t filter all these creatures from your system. Only using the filters on a part-time basis is one method to prevent removing these tiny creatures. Also, the use of carbon and other media such as Purigen or Chemipure can be beneficial in removing various organic and inorganic compounds. Canister filters, HOB filters can also be useful but must always be cleaned regularly.
Choosing the correct mixture of livestock can be an important factor in creating a stable marine habitat. For example, an abundance of snails will help keep the tank clean. Certain type snails will also assist in sifting the sand to help prevent having "stagnant" areas of the sandbed. Sick or dying snails can be eaten by crabs and bristleworms and their shells can provide new homes for hermit crabs. Fish such as the Foxface, certain Angels, Lawnmower Blennies and others will graze on algae growths in the tank often preventing the spread of nuisance algae. In tanks with an overabundance of Bristleworms, the strategic addition of a Hawkfish can help keep their numbers manageable.
Diversity of corals (SPS, LPS, and soft corals) provides an additional challenge. Certain LPS like Frogspawn can have tentacles that can be far reaching. If the tentacles come in contact with other corals, one or both corals may be damaged by the contact. Soft corals can emit chemicals (allelopathy) in response to nearby corals. All these type corals need to be placed in areas where they will not have to compete for space. They should also be allowed room for future growth.
Again, anemones are only to be considered by those who have studied the specific requirements of these animals. If given the proper environment, anemones can be an awesome addition to any aquarium.
In Conclusion
While the two setup types described above are possibly the most popular type setups, there is an unlimited number of variations. Tanks are often created that incorporate ideas from each type setup. Proper tank planning and research can result in the most pleasing viewing by the tank owner and will help the aquarist provide an appropriate environment for the tank inhabitants.