In the reefkeeping hobby, many people take great pride in being able to bring in the ocean's denizens and have them living happily in their own homes. All the time, hobbyists strive to make their aquariums as natural as possible to mimic the natural habitat. However, one can never forget that you are keeping organisms in a place that is unnatural to them. The only way we are able to do this effectively is through the range of gizmos and gadgets invented to help make the job easier. In this section we shall discuss the technology and equipment that should be considered.
Keep in mind that the title of "equipment" is a vague one; this section will also discuss other non-living elements such as decor.
There are a number of options to house your planned occupants in. Throughout the ages, fish have been kept in bowls, aquariums, ponds, and just about anything else that can hold any bit of water. Choosing what sort of container you wish to house your fish in is an important decision. However, for the purposes of marine aquaria, the aquarium is the most common choice.
Aquariums come in all sorts of shapes and sizes. What's the right one for you? There are a number of things to consider, such as volume, shape, footprint and surface area, and material. All of these variables play a role in deciding what sort of aquarium you should get, as well as others such as cost.
In terms of volume, bigger is almost always better. In the ocean, mobile organisms are not restricted by having walls around them, and are free to move just about wherever they please. Fish, just like you and me, feel stressed in an environment that is too small for them; especially if you wish to keep more fish or larger species of fish, a larger tank gives you more space to work with. It is easy to overcrowd an aquarium that is too small. Another point about volume is that the more water there is, the more water exists to dilute any substances in the water. These substances may be waste products from your organisms, uneaten food left over, or some sort of accident. Having more water in your aquarium gives you more leeway in a lot of respects. In many ways, having a larger tank makes it easier as you can make a few more blunders and not have disastrous consequences. For this reason, small marine aquariums are actually more difficult to maintain; such aquariums are known as "Nano" Tanks or Reefs. There is no black-and-white division between "Nano" Tanks and your standard sizes, but beginners should avoid an aquarium of 20 gallons or lower. The beginner reefkeeper should consider a mid-sized aquarium of around 55 gallons. In the situation of aquarium size, there are very few situations where bigger is not better for your fish.
Aquariums come in all sorts of shapes. The standard aquarium shape is rectangular. However, other shapes exist as well. The most common other styles seen are hexagonal, where the base is a hexagon rather than a rectangle, and bowfront, where the front pane of the aquarium bows outward. Of course, the aquarium can also be custom-built to any shape specification. For the most part, shape of the aquarium is merely aesthetic, but the footprint, or surface area, is also an important factor.
Footprint and surface area are important to consider. The footprint is the amount of space that the tank's stand will take up on the floor. The surface area in this situation means the surface area of the water in the aquarium. In most aquariums, these two are just about the same. Of course, the footprint must be considered for looking for a proper location in the house to see if a fish tank will fit. However, the surface area is also important for two reasons. One, the surface is how gases such as oxygen enter and leave the water. Therefore, with more surface area, you get better gas transfer and therefore you can house more animals. Another reason is that many fish spend more time swimming horizontally than vertically; this means that the more surface area you have, the more swimming space is available. Because of these reasons, if you are comparing two aquariums of the same volume, you should opt for the one that has more surface area, as it will provide better gas transfer and more capacity for organisms overall.
Material of the aquarium can make a difference as well. Today's aquariums are normally built out of either glass panes bonded with silicone or acrylic. Both types have their advantages and disadvantages.
Glass is cheaper, more common in many standard shapes, and does not scratch as easily as acrylic. However, acrylic does not bend light in the same way as glass, giving a much better view of the inhabitants; for this reason, acrylic is common in many public aquariums where the aquarium wall must be very thick and so the bending of light would make it more difficult to see the organisms. Also, acrylic is less prone to leaking. This is because glass is bonded together by silicone (and visibly so, if you find silicone an eyesore). However, the seams of acrylic aquariums are bonded together by acrylic; in effect, an acrylic aquarium can be a single piece of acrylic, making it stronger. Acrylic is also lighter than glass. Acrylic also can insulate the water better than glass can. On the other hand, acrylic is often more expensive and scratches more easily (though the scratches on acrylic are much easier to fix than scratches on glass). Also, though acrylic is less prone to leaking and breaking than glass, water will cause acrylic to bow out; the stand must support the entire bottom surface of the aquarium, instead if just the edges for a glass aquarium. The choice is up to the hobbyist.
Ponds are much rarer in the marine hobby, but they do exist. A pond is usually considered to be housing that is on or sunk into the ground; usually, you are not able to see through the sides of a pond. Therefore, for a larger volume of water, a pond can be cheaper and more feasible than an aquarium. For species of animals such as stingrays or sharks that can be viewed well from above, a pond is a possible choice.
Water Quality 
Filtration is a method or process by which system inputs are transformed or exported from the reef tank to help maintain livestock viability. There are many types of filtration methods, including Mechanical, Biological, and Chemical.
Mechanical filtration refers to passing water through some sort of filtration media that will strain particles out of the water. Chemical filtration refers to using some sort of chemical or substance such as activated carbor to pick up or remove substances from the water. Biological filtration refers to using bacteria, like those important to the Nitrogen Cycle, to help remove some substances from the water. Many filtration systems have some combination of two or all three of these methods.
Protein Skimming 
Protein Skimming is a water purification method where large molecules such as proteins are actually removed from the aquarium before they have the chance to break down. It works by creating a foam or a froth, similar to the action of waves at the shore.
Deep Sand Bed 
A Deep Sand Bed, sometimes shortened DSB, is a form of biological filtration. A sand bed that is at least 4" deep is considered a deep sand bed. It functions by having an extremely high surface area near the upper layer of sand, which serves as a living space for aerobic bacteria that will convert ammonia to nitrites and then to nitrates. However, because the sand is deep, oxygen will not reach the lower layers, forming anaerobic pockets. In these pockets, anaerobic, denitrifying bacteria will form that allow for the conversion of nitrates into nitrogen gas.
Reverse Osomosis, Deionized, and Diatomaceous Earth 
All of these are different ways of purifying water before you even mix the salt. Tap water is relatively impure, and to make sure we have the very best water, there are several purification methods available. Many people actually swear by using such pure water to mix their salt with, as it can help prevent many problems.
Water Movement 
Although often filtration provides a source of water movement, in the case of marine aquaria it is often not enough. Proper water movement is accomplished through the use of either powerheads or special machines that simulate waves.
Temperature Control 
Most of the organisms in the hobby do not live in room temperature conditions. The general majority of organisms originate from tropical locations, and a minority come from coldwater habitats. It is important to maintain the correct temperature so that your aquarium inhabitants are comfortable.
The aquarium heater is necessary to maintain an aquarium at tropical conditions of about 75 degrees Fahrenheit to 82 degrees Fahrenheit (24 °C to 28 °C). It is a simple glass or plastic tube containing coils of metal wire that heat up when electricity runs through it. A thermometer is built into the heater so that it shuts off at the appropriate temperature. Aquarium heaters are labeled for wattage. A general guideline is 5 watts per gallon; this can be achieved with either one heater or with multiple heaters. For many smaller aquariums, one is enough. However, having multiple heaters is a good idea in many situations, especially for larger aquariums. One, it allows you to spread out the sources of heat in the aquarium so it is not concentrated all in one spot. Secondly, in the event a heater fails or malfunctions in some way, there are other heaters to back it up.
When placing the heater in the aquarium, one should try to place them horizontally or angled in some way near the bottom of the aquarium, rather than vertical. To understand why, think about convection, or the phenomena of warm substances rising. If a heater is placed vertically, warm water at the bottom of the heater rises up and stays next to the heater. However, if the heater is placed horizontally, warm water will rise up away from the heater, allowing the heater to be more efficient. Because it is better to have the heater placed horizontally in this way, submersible heaters are a better choice than heaters that hang onto the edge of the aquarium.
Something else to consider is safety for your organisms. As a heater, one should expect this apparatus to get hot. However, sometimes organisms will touch the heater for just a little to long and burn themselves. This is especially a problem for softer-skinned organisms such as stingrays. There are some options for this. One is to purchase a heater guard; you merely put the heater guard on the heater tube so that the organisms can't touch the tube directly. Another option is to place the heater in the sump. Having the heater in the sump has the advantage of not only being out of the way of your aquarium inhabitants, but also being out of sight.
Unlike the commonplace heater, the chiller is a more expensive piece of equipment, but necessary if one is considering keeping coldwater species.
Normal Output 
Very High Output 
Metal Halide 
Monitoring Gadgets 
Temperature is one of the many important factors that needs to be monitored. A thermometer can be placed anywhere in the tank, but keep in mind that if circulation is slow, the temperature is likely to be different in some areas of the aquarium. The thermometer can also be placed in the refugium.
Thermometers can come as a sticker that attaches to the outside of the aquarium. Though convenient, these thermometers can be more inaccurate.
Test Kits 
One of the considerations for the marine aquarium is what to put on the bottom of the tank. In some cases, some people opt for a bare-bottom tank without a substrate, as this can be easier to clean. However, such a set-up is less natural, and so most aquarists decide to put some sort of substrate in.
Crushed Coral 
Crushed coral has been the traditional substrate for marine aquariums for years. The degree to which the coral is actually crushed can vary, but otherwise they are the same. Because crushed coral is made up of the limestone skeleton of coral, it has the advantage of raising the hardness of the water, which helps resist pH decrease.
Coral Sand and Aragonite-based Sand 
Coral sand and aragonite sand are both about the same. Like crushed coral, they both contain elements that help raise the hardness of water. Unlike crushed coral, though, the sands are much finer. Hey
Live Sand 
Sand sold as Live Sand is usually a coral sand that supposedly contains bacteria or other living organisms in it, similar to rocks sold as Live Rocks. The sand itself is not alive, but it contains living organisms. It has the advantage of already harboring the bacteria necessary for good biological filtration on top of being able to raise the hardness of water.
Live Rock 
Maintenance Equipment 
There are times when the aquarist themself has to get down and dirty to keep the tank running smoothly, and here are some of the tools of the trade.
Gravel Vac 
The gravel vacuum is a contraption that uses the concept of siphoning. By starting a siphon of water from the tank to another location, the gravel vac begins to suck up water and whatever is nearby. This is useful to help clear the substrate of particulate matter.
Gravel vacs come in numerous styles. One of the most common forms is a gravity-driven siphon, in which water is pulled from the tank to a bucket or something else that is lower than the aquarium. Another is a Venturi-driven siphon, which works by hooking up to the sink with a special attachment; by turning on the sink, a vacuum is created in the tube which sucks the water from the aquarium. Other, less common forms include hand-pumped or even battery-powered.
Gravel vacs, as somewhat hinted by the name, are mostly only effective in mid-sized substrates. Sand can be sucked away by a gravel vac, making them less effective if the substrate is sandy. Also, if there are a large number of rocks, the gravel vac can have a hard time reaching around to tighter corners.
Algae Scraper 
Algae scrapers are items used to scrape away algae, usually off of the aquarium glass.
Algae scrapers also can come in a variety of forms. One form is a scraper on the end of a long stick, slightly reminiscent of a window squeegee and serves approximately the same purpose: to clean glass. However, the other option is the magnetic algae scraper, in which the aquarist handles a magnet on the outside, and another magnetic scraping piece follows inside the aquarium. There are even magnetic algae scrapers that float in case the magnets somehow get too far away from each other, making retrieval much easier.
One must be careful with algae scrapers and acrylic, as particulate matter such as sand caught in the scraper can cause scratches.
Tried and true, here are a few things that aren't sold at your local fish store that just might come in handy.
In the marine hobby, when we say eggcrate, we're not talking about the cartons eggs actually come in, nor are we talking about bumpy foam pads. What we mean by eggcrate are eggcrate grilles that are often used for air vents and fluorescent lights; plastic that forms criss-crossing lines.
So what does eggcrate have anything to do with marine aquaria? Well lots. In fact, it can be the very foundation of a reef, pun intended. Eggcrate is placed underneath the rocks and buried in the substrate. By having eggcrate, you spread out the weight of the stones over the bottom pane of the glass.
You can purchase eggcrate at a hardware store.
Turkey Baster 
No, it's not Thanksgiving. A Turkey Baster is actually a useful tool in the hobby. Using a turkey baster, you can suck up some small stuff without disturbing too much of the tank. On the other hand, you're able to target food or anything else at a certain organism without it having to float all over the tank. The ability to target with a turkey baster can actually become quite handy. Of course, don't use a turkey baster you're going to use for food with your aquarium, and vice versa.
The quintessential cleaning tool, a toothbrush lets you get into those small places that is difficult to reach with just about anything else. Keeping an old toothbrush handy can help you out in a tight spot.