Title graphic for Sea and Sky's Saltwater Aquarium Guide

 Aquarium Equipment Guide

When is comes to equipment, there are a lot of choices available to today's marine aquarium hobbyist. The only real limit to the hobby is the size of your pocketbook. Our aquarium equipment guide will help guide you through the maze of equipment and accessories available in the saltwater and marine reef aquarium hobby, including water testing equipment, temperature control, filters, chemicals, and accessories. Some of this equipment is optional, but can make your hobby easier and more enjoyable when you are ready to move on to the next level.


A hydrometer is one of the most important instruments in the marine aquarium hobby. It is used to measure the specific gravity the aquarium water, which will tell you how much salt is in the water. The hydrometer uses a floating dial that will indicate the proper reading when filled with water. For a marine aquarium, the specific gravity should be maintained at close to 1.026 with the water temperature at 78 degrees F (26 degrees C).

pH Monitors

pH Monitors provide the ability to continuously monitor the pH of your aquarium water. They consist of an electronic device with a digital readout connected by a wire to a probe. The probe can be placed in the water, usually in the sump, to provide a continuous readout of the water's pH. The units must be periodically calibrated using special calibration fluids. Once properly calibrated, pH monitors give extremely accurate readings and provide a convenient alternative to using chemical test kits.

RO/DI Filters

Water quality is a major concern for the marine aquarium hobbyist. The quality of tap water in most metropolitan areas is not good enough for use in marine reef aquariums containing delicate corals and invertebrates. RO/DI filters consist of a membrane that filters the water through a process known as reverse osmosis (RO). The water also passes through a number of canister filters including a deionizer (DI). RO/DU units can provide extremely pure water. All though they do require an initial upfront investment, they are and much more convenient cheaper in the long run than buying bottles water or purchasing premixed water from an aquarium store. RO/DI units can also be purchased with built-in Total Dissolved Solids (TDS) meters to provide a digital readout of water quality at each stage of the filtration process. Filters must be replaces periodically but can usually be found online at significantly reduced prices. If you are looking planning to keep invertebrates and corals in your aquarium then an RO/DI filtration unit is definitely a highly recommended piece of equipment.

Salinity Monitors

Salinity monitors are the most expensive option for checking the salinity of saltwater. They consist of an electronic device with a digital readout which is connected by a wire to a probe. When the probe is exposed to water, the salinity will display in the digital readout. Salinity monitors must be periodically calibrated using a special calibration fluid. Once calibrated, they can provide extremely accurate readings. Their biggest advantage over hydrometers and refractometers is that they can provide continuous real-time readings. The probe can be left in the water, usually in the sump, to provide a continuous readout of the water's salinity.

Salinity Refractometers

Salinity refractometers are devices that are used to measure and monitor the concentration of salt in saltwater. They are available as an alternative to the hydrometer. They do cost a bit more but are usually more durable and can give more accurate readings. Hydrometers can be difficult to work with and can give false readings if you are not careful to keep bubbles off the floating swing arm. Once calibrated, refractometers can provide extremely accurate readings. Many aquarium retailers offer a special fluid that can be used to properly calibrate the refractometer.

TDS Meters

A TDS meter is a small, electronic device that can measure the Total Dissolved Solids (TDS) in a sample of liquid. TDS meters are useful for testing your aquarium water's purity. Ideally, fresh water used for your aquarium should have a TDS reading of 0 parts per million (ppm). Most experts recommend that water used for a marine fish aquarium be below 30 ppm. For a marine reef aquarium, the reading should be below 10 ppm. If you filter your own aquarium water, a TDS meter is a necessity. TDS meters are fairly inexpensive and can be found at most local aquarium retailers.

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A thermometer is a necessary part of any aquarium setup. Aquarium water must be maintained within a limited temperature range to avoid stressing the animals. The least expensive option is a simple glass thermometer that can be attached to the glass inside the aquarium using suction cups. Digital thermometers are also available that can be attached to the outside of the tank. They have a wire with a probe that is placed inside the aquarium. Many digital thermometers also have an alarm that can be set to go off if the temperature gets too high or too low. A marine aquarium should be kept within a range of 76 degrees F (25 degrees C) and 82 degrees F (28 degrees C). If your aquarium temperature frequently fluctuates outside this range, you may need to add a heater and/or chiller to the system.


Heaters must be used to maintain the temperature of an aquarium during the winter or in cold climates. Aquarium heaters can be purchased at local pet shops and specialty aquarium stores. Heaters come in different sizes. When purchasing a heater, make sure you get one that is made for the size of the aquarium you have. The general rule is 25 watts for every 5 gallons (19 liters) of water in the aquarium. If you have a very large aquarium you may need to use two heaters. With heaters, it is better to get one that is too big than to get one that is too small. Aquarium heaters come in several different types.

Immersible Heaters

Immersible heaters heat by direct contact with the water. They are usually the cheapest option for heating an aquarium. They cannot be completely submerged under the water. This can make them difficult to place in the tank because they must be placed with their tops out of the water.

Submersible Heaters

Submersible heat by direct contact with the water. They can be completely submerged under the water. This makes them a more popular choice with aquarium hobbyists. The do cost a little more than immersible heaters, but their flexibility makes them worth it. Submersible heaters are available with both glass and metal bodies. The glass heaters are cheaper, but the metal heaters are much more durable and will last much longer.


If your aquarium temperature is running too hot due to a warm room and/or aquarium lights, a chiller can help keep the water cool. A chiller is a small refrigeration device that is connected to the aquarium to cool the water. If you are planning to keep coral in your aquarium, then a chiller will be necessary in warmer environments. Chillers come in three types.

Thermoelectric Chillers

Thermoelectric chillers provide a quiet and energy efficient way to cool small aquariums. Thermoelectric chillers work by converting electricity directly into cooling power. They are intended for aquariums of 55 gallons (208 liters) or less.

Drop-In Chillers

Drop-In Chillers have a probe that is placed in a sump. The probe is connected by a two or three foot hose to a refrigeration box that sits outside the aquarium cabinet. Drop-in chillers are easy to add to existing systems because they require no plumbing. They make an ideal choice for systems with limited space. They do take up space in the sump and the probe can sometimes be hard to work with. They are available in different sizes and can be used with large aquariums.

In-Line Chillers

In-Line chillers must be plumbed in-line with the aquarium system plumbing. They are usually placed between the sump and the return line to the aquarium. They require more space than drop-in chillers and should be included in the original set-up plans for a new aquarium. They are more convenient than drop-in chillers since there is no probe taking up space in the sump. They are available in different sizes and can be used with large aquariums.

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Calcium Reactors

Calcium reactors are optional pieces of equipment that can maintain the level of calcium in the aquarium. For coral reef aquariums, a calcium reactor can be a valuable tool. As the animals in an aquarium grow, they remove calcium from the water. This calcium must be replenished. One way to add calcium is through regular water changes using a reef aquarium approved salt mix. Liquid calcium additives are also available. Water testing and manually adding calcium are usually enough to maintain appropriate levels. But some hobbyists, especially those with large reef tanks, prefer the added security that a calcium reactor can provide. The calcium reactor will help maintain consistent levels of calcium and alkalinity. This can be important when keeping sensitive corals.

Phosphate Reactors

Phosphate reactors are optional pieces of equipment that can reduce the level of phosphates in the aquarium water. Phosphates are organic compounds that build up in the water as a result of excess fish food, fish waste, and other organic sources. Phosphates contribute to the growth us unwanted algae in the aquarium and in extremely high concentrations, they can be toxic to fish and invertebrates. Phosphates can usually be controlled by routine maintenance, regular cleaning, and regular water changes. Phosphate reactors can also help remove phosphates from the water. They consist of a plastic tube that is filled with a phosphate removal medium and is connected to a small pump in the sump. They are fairly inexpensive and easy to install. They can help keep phosphates under control if you intend to keep a lot of livestock in the aquarium.

Protein Skimmers

Protein skimmers are devices used to remove organic waste from aquarium water. They typically work by mixing water with thousands of tiny bubbles. The bubbles cause the waste to rise into a cup where it can be collected and discarded regularly. Protein skimmers are highly recommended for marine aquariums because they can help to keep the water clean and pure. Skimmers come in different sizes. The larger the skimmer, the more waste it can remove from the system. With skimmers, bigger is always better. Skimmers are typically installed in the sump, all though there are some models that can be mounted on the back of the tank. When purchasing a skimmer for your aquarium, make sure you get one that is large enough for the size of your tank and the number of animals (the bioload) you have.

UV Sterilizers

Ultraviolet (UV) sterilizers are devices that use high intensity ultraviolet light to remove microscopic contaminants from the water. UV sterilizers can remove bacteria, fungi, viruses, algae spores. They are usually hooked up inline with the return water. As the water passes through the device, the microscopic organisms are destroyed by the ultraviolet light. UV sterilizers can be beneficial for preventing diseases and algae blooms in fish-only aquariums. They are usually not recommended for marine reef aquariums because they can also destroy beneficial organisms such as plankton and nitrifying bacteria. They can be expensive, depending on the size of the aquarium. Ultraviolet light is dangerous to your eyesight so the unit should always be unplugged when working on it. If you are planning to set up a saltwater fish aquarium with no invertebrates, a UV sterilizer may help to prevent diseases and help to keep your aquarium free of nuisance algae.

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A trip to any aquarium specialty store may reveal a wall of bottles and jars that resembles Doctor Frankenstein's chemistry lab. There are hundreds of commercial chemicals and supplements available for the aquarium hobby. Most of these are unnecessary and, depending on who you talk to, some are just flat out snake oil. Dechlorinators can be useful if you absolutely must use tap water. Ammonia removers can be useful in an extreme emergency if you experience an ammonia spike, but it should be used sparingly. Overuse can starve the nitrifying bacteria in your system and cause it to recycle from scratch. As long as you perform your monthly water changes using an good quality salt mix and pure, filtered water, you really should have no need to add chemicals to your marine aquarium.


A wide variety of aquarium supplements are available from your local aquarium retailer. The sheer variety can be confusing to those who are new to the hobby. If you are diligent in performing your scheduled water changes using a good quality salt mix, you really should have no need to add supplements to your tank. That being said, there are some basic supplements that are useful for marine reef aquariums. Supplements for calcium and alkalinity can be useful for maintaining proper levels. Care must be taken to test the water regularly to maintain the proper levels. Other supplements that are used by more advanced hobbyists include magnesium, iron, silicate, iodine, strontium, and borate. These supplements should only be used by advanced aquarists who know what they are doing. Adding too much of these elements can cause serious problems in a reef aquarium. The general rule of thumb for supplements is don't add anything to the aquarium that you cannot test for.

Salt Mixes

Aquarium salt mixes consist of sea salt mixed with other essential elements such as calcium, magnesium, bromine, strontium, and silicon. These mixes are intended to simulate the composition of natural sea water as closely as possible. There are several brands available and two main types. Standard salt mixes are suitable for fish aquariums. They are the least expensive option. Most manufacturers also offer a reef mix, which contains additional elements necessary for the growth of corals. These mixes cost more but will generally yield better results when used for a marine reef aquarium. Instant Ocean is one of the more popular brands. They make a standard mix as well as a reef mix called Reef Crystals.

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Powerheads are small, submersible pumps that can be placed inside the aquarium to provide additional water movement. They can be attached to the glass using suction cups or magnets. Powerheads create a current in the water and can help prevent the formation of dead spots, areas with little to no water movement. Coral requires water movement to help the stationary animals expel waste products. For marine reef tanks with coral, powerheads are a necessity. Most experts recommend adding two powerheads in a reef tank, on at either end of the tank at different heights. This will create current to benefit the coral and provide a natural-looking environment. There are devices available that can be hooked up to the powerheads to pulse them on and off to create a natural wave action, which can be beneficial to coral because it recreates the natural waves on the coral reef.

Test Kits

Water test kits are an essential part of every marine aquarium system. Your water should be tested once every week. For fish-only aquariums, you should test ammonia, nitrite, nitrate, and pH. For marine reef aquariums, you will also need to closely monitor calcium and alkalinity. Additionally, you should also check phosphate levels. Test kits are available from several manufacturers and can be found at your local aquarium retailer and most pet stores. Many local fish stores (LFS) will offer to test your water for free. But even if you decide to test your water this way, you should always keep test kits on hand for emergencies. This way you can take immediate action if something goes wrong and your local store is closed.

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