Here is a list of terms commonly used in the aquaria hobby. Bolded words are defined in this FAQ. If you can think of a word (or words) that needs to be added, post it here along with a definition (if you know what it is), and I will edit this list to include your word.
Absorption - The process of taking a substance in through pores or interstices. For example, a sponge absorbs water.
Adsorption - The accumulation of gases, liquids, or solutes on the surface of a solid or liquid. For example, activated carbon removes certain contaminants from water through adsorption.
Ammonia – a chemical (NH3) present in fish waste. Ammonia is highly toxic to fish, and any detectable amount in your aquarium water is a problem. A class of bacteria “eats” ammonia and converts it into nitrites. If your aquarium is properly cycled, you will have no detectable ammonia. There are two types of ammonia test kits available on the market. These are the one-part test using Nessler’s Reagent, and the two-part salicylate-based test. If you use a water conditioner that removes chloramines from your tap water, you should purchase a salicylate-based test. This is because Nestler-based tests will give false ammonia results in combination with the chemical that removes chloramines.
Acid – a water-based solution whose pH is less than 7.0.
Acrylic – A clear, somewhat flexible material used to construct some aquaria. It is also known by the brand name “Plexiglass”. On the positive side, acrylic is much more shatter resistant than glass, is lighter, optically clearer, easier to bend and shape, and can be made to look “seamless”. On the negative side, acrylic is more expensive than glass, scratches easily, and because of its greater flexibility, requires a thicker tank wall.
Albino - Albinism is the result of a genetic dysfunction/mutation that prevents the production of melanin pigment. Melanin is responsible for all dark coloration.. See Lutino.
All-Glass Aquarium – A popular manufacturer of aquaria. Their subsidiary, Oceanic, manufactures a premium line of aquaria.
Aquaclear – A brand name of Rolf C. Hagen, Inc. Aquaclear (AC) filters are a popular line of power (hang on the back) filters.
Base – A water-based solution whose pH is greater than 7.
Bioload – represents the amount of work the nitrifying bacteria in your aquarium and filter media have to do to eliminate ammonia and nitrite from the water. It is roughly equivilant to the amount of waste being produced in your aquarium. It is also roughly proportional to the total weight of fish and other aquatic organisms in your aquarium.
Bio media – Material in your filters that will host colonies of nitrifying bacteria. This material is generally very porous to allow a lot of surface area for the bacteria in a relatively small volume of material.
Buffer – a chemical that, when dissolved in water, tends to keep the water at a partcular pH. If you want to change the pH of water, you must first “use up” the buffer before the pH change can occur. Unbuffered water is subject to wide pH fluctuations, which are quite stressful to your fish.
Chlorine – a greenish yellow toxic, pungent gas (Cl) that is used in some modern water treatment works to sterilize tap water. Chlorine is highly toxic to fish and other aquatic organisms, and must be removed from water that you are adding to your tank. This can be done with commonly available dechlorinators, or by allowing the water to sit in an open container for at least 24 hours. Check with your local treatment works to find out what disinfectant is used in your tap water.
Chloramine – a colorless pungent liquid (NH2Cl) that is used in some modern water treatment works to sterilize tap water. Chloramine is highly toxic to fish and other aquatic organisms, and must be removed from water that you are adding to your tank. This can be done with commonly available water conditioners. Make sure that the bottle indicates that the conditioner removes (or neutralizes) chloramines. Check with your local treatment works to find out what disinfectant is used in your tap water.
Cycle – When used as a noun, this is short for the nitrogen cycle. When used as a verb, this refers to the process of colonizing your tank and filter media with bacteria that complete the nitrogen cycle. A discussion of the nitrogen cycle and of cycling your tank can be found here.
Calcium carbonate – A chemical (CaCO3) that acts as a natural pH buffer in water. If your water is high in calcium carbonate, its pH will tend to be higher, and more resistant to change. If your water is low in calcium carbonate, its pH will tend to be low, and less resistant to change. Water that is high in calcium carbonate is said to be alkaline. An easy way to test for alkalinity is with a “KH”, or “carbonate hardness” test kit. These kits commonly give resulte in “German Degrees”. One German Degree is equal to 17.3 ppm calcium carbonate.
Cannister filter – A category of filters that typically sit outside of the aquarium, normally inside the stand. They consist of a large plastic container in which various forms of media can be placed. On top of the container a lid is equiped with the impeller housing, and fittings for the intake and discharge hoses. Some cannister filters contain smaller trays inside of the large container. These trays are used to separate layers of media, and make the filter easier to service. A cannister is connected to the aquarium through two flexible hoses, one for intake, and one for discharge. At the intake side, is a long tube that extends down into the aquarium water, and has a strainer at the end. At the discharge side is some type of device to disperse the flow. Most cannisters use a spray bar to disperse the flow. Caudal fin – The “tail” of the fish.
Chemical media – filter media that removes chemicals from the water. This is most commonly achieved by adsorption. Carbon is the most common chemical media. In a healthy, well-maintained tank, carbon is optional. It can be helpful if your tap water has unusual odors or colors. It can also be used to remove medecines after treatment, or unwanted chemicals that are accidentally spilled into the aquarium.
Dorsal fin – The fin running along the top of the fish parallel to the spine.
Eheim – A German manufacturer of pumps and aquaria products. Eheim is well known for extremely high quality equipment.
Emperor – A popular brand of filters made by Marineland. They feature “biowheels”, which expose the nitrifying bacteria to air and water on an alternating basis, allowing a denser growth of bacteria on the biowheel material.
Energizer – an electrical device connected to a filter that creates alternating magnetic fields inside the impeller well.
Filter – A device that draws water from your tank, treats it in some way or ways, and then discharges the treated water back into the tank. There are three major forms of filtration used in fishkeeping. These are mechanical filtration, biological filtration, and chemical filtration. In a healthy tank, mechanical and biological filtration are essential.
Flashing – a common symptom of external parasite infections. Characterized by the fish rubbing their bodies on objects in the aquarium.
Glass – a material comonly used to construct aquaria. Glass is cheaper, and more scratch resistant than acrylic, but shatters readily, is less optically clear, and is much heavier than acrylic.
Gravel vacuum – A device that uses the vacuum created by flowing water to suck mulm out of the substrate. This can be a simple siphon hose with a large-diameter regid plastic tube at one end, or a Python.
Hagen – A brand name of Rolf C. Hagen Inc, a manufacturer of equipment and supplies for the aquaria (and other pets) trade. Some of their brand names include Hagen, Aquaclear, Fluval, and Nutrafin.
HOB filter - HOB stands for “Hang On the Back”. This term is interchangable with power filter.
Hole in the head disease (HITH) – A form of lateral line erosion disease caused by poor nutrition and poor water quality. Here is a detailed discussion of the condition.
Ich – the common name for the Ichthyophthirius parasite, which is commonly present in aquarium water. Healthy, unstressed fish are normally able to fight off this parasite, and do not contract ich. However, stressful conditions can reduce the resistance of your fish to ich, and other parasites and diseases. Signs that your fish has contracted ich include flashing, gasping for air at the surface, and small white specks on your fish’s body.
Impeller – A device inside of a filter that causes the water to flow. An impeller consists of a shaft with a cyllindrical magnet and a paddle wheel attached. Impellers are driven by an energizer.
Lutino - A lutino is an oscar that is mostly white, but with some coloration. These fish are commonly sold in the trade as “albinos”. For example, the oscar shown in the upper left-hand corner of this site is a lutino. See Albino.
Marineland – a manufacturer of aquaria equipment and supplies. Some of Marineland’s brand names and trademarks include Marineland, Emperor, Penguin, Magnum, Perfecto, Instant Ocean.
Mechanical media – material in your filter that is designed to remove solid particles from the water. Mechanical media is generally subdivided into coarse, medium, fine, and micron, with each categroy removing progressively smaller particles from your water. If your filters allow it, you should always place coarser mechanical media before finer media. This will make your finer media, which is typically more difficult to clean, last longer before it clogs.
Mulm – a term applied to the decaying waste material and uneaten food that collects at in the substrate of an aquarium. Mulm is removed through regular vacuuming of the substrate with a siphon hose or Python.
Nitrate – a salt of nitric acid containing the NO3- radical. Nitrates are the end product of the nitrogen cycle. Over time, nitrates will build up in a cycled tank, and will need to be removed through partial water changes.
Nitrite – a salt of nitrous acid containing the NO2- radical. Nitrites are extremely toxic to fish, and any amount of detectable nitrites in your water is a sign of a problem. A class of bacteria “eats” nitrites and converts them into nitrates. If your aquarium is properly cycled, you will have no detectable nitrites.
Nitrogen cycle - A natural process by which bacteria convert waste products from ammonia to nitrites to nitrates. You can read more on the nitrogen cycle here.
Nitrifying bacteria – the bacteria that colonizes in your aquarium and filter media and removes ammonia and nitrites from your aquarium.
Oceanic - A subsidiary of All-Glass Aquarium. A manufacturer of premium glass aquaria.
Ovipositor - An extension of the female genital orifice of certain fishes. This organ is used to deposit eggs on a surface so that the male can fertilize the eggs.
Partial water change – The act of removing some of the water from the aquarium and replacing it with fresh, treated tap water. Normally, the inside of the tank is cleaned with a gravel vacuum during this process.
pH – a way of quantifying the relative acidity of water. The “p”, which should always be in lower case, stands for a latin word “ponus”, which means “power”. Chemists use the lowercase p to indicate the negative common logarithm of a quantity.The “H” stands for the latin word “Hydronius”, or, in english, Hydrogen. So the term “pH” refers to the negative common logarithm of the concentration of hydrogen ions in the water. If this concentration is relatively high (greater than 10^-7 moles per liter), the water is acidic, and the pH will be less than 7. If the concentration of hydrogen ions is relatively low (less than 10^-7 moles per liter), then the water is basic, and the pH will be greater than 7. Neutral water has exactly 10^-7 moles of hydrogen ions per liter, and has a pH of 7. Some fish (such as african rift lake cichlids) are from basic waters, and prefer a higher pH, while other fish (such as Oscars) are from acidic waters and prefer a lower pH. Regardless of a fish’s preferred pH, it is very important to maintain a stable pH in your aquarium. This is done with regular water changes to replenish the natural buffers, and sometimes through the addition of materials to the aquarium and/or filtration that will buffer the water to a desired pH.
Plexiglass – a brand name of acrylic.
Power Filter - Also called Hang on the back, or HOB, these filters hang on the back of a tank. Generally, these filters have limited media capacity, and are intended for smaller tanks, and for providing back-up to cannister filters on larger tanks. Popular power filter lines include Emperor and Aquaclear.
Python – A brand name for an aquarium maintenance device. It consists of a gravel vacuum at one end, a long clear flexible hose, and a siphon pump that ataches to a water faucet. This device can be used to automatically drain and refill an aquarium without using buckets.
Spray bar - A long tube at the discharge end of a filter that is drilled with holes at even intervals, and plugged at the far end. Spray bars are intended to disperse the flow of water coming out of the filter.
Water conditioner – Various chemicals sold in the aquaria trade. These are generally intended to be added to tap water to make it safe for your fish. The main thing a conditioner must do is remove chlorine and/or chloramine from your tap water.