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Vocab & Jargon L-Q

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Light Emitting Diode, these lights are popular in the saltwater aquarium hobby for several reasons. They consume a relatively low amount of energy, produce little heat, run quietly, and are often programmable.

Photon V2+ LED Lights


Local Fish Store

Live Rock

Live rock, either human-made, mined, or pulled from the ocean, that is is shipped to you either “wet” or “dry”. It is called live rock, not because it necessarily comes with live bacteria, but because it will be colonized during the cycling process.

Live Sand

Live sand comes in various types and grain sizes, and is usually shipped “wet” and full of healthy bacteria to help cycle your tank.

wet live sand for saltwater aquariums


The brand name of a modular hose system often used provide directional flexibility in the return plumbing.

Low-Iron Glass

High clarity glass made from silica with a low iron content. Offers a more “clear” viewing experience as it removes the grean/blue tint found in regular glass. Sold under the brand name Starphire Glass.

© My First Fish Tank


Large Polyp Stony Corals

© My First Fish Tank, 2019


Macro Algae such as chaetomorpha and caulerpa are used in saltwater aquariums to help remove phosphate from the water column, as well as to provide a safe place for amphipods and copepods to breed. Macro algae is usually grown in a refugium section of a sump with its own separate light, and trimmed back from time to time as it grows.

ball of green chaetomorpha macroalgae in clear bottle

Magnetic Algae Scraper

Any type of algae scraper that uses a magnet to connect the dry and wet side.

Marine Ich

Also called Marine Ich, Ick, or White Spot Disease, it is a common saltwater fish disease. Ich can cause high mortality rates in your fish if not caught early. The most common treatment for Ich is copper.

© Marine Depot

Marine Velvet

Also known as velvet or gold-dust disease, Marine Velvet is highly contagious and often fatal. Caused by photosynthetic dinoflagellates, treatment usually involves dosing Cupramine in a hospital tank and leaving the lights off for the course of treatment. Oftentimes with Marine Velvet, once you notice it is often too late to save your fish.

By Mydigitalife - Own work, CC0,

Mechanical Filtration

Any form of filtration that physically removes particles from the water. The most common types of mechanical filtration in the saltwater aquarium hobby are filter socks and sponges.


Comes in three types: mechanical, chemical, and biological.

Mechanical media would be things like sponges, poly-filters, and filter socks.

Chemical media consists of items such as GFO (Granular Ferric Oxide), activated carbon, and purigen.

Biological media can be live rock, bioballs, or ceramic plates.

The easiest way to think about media is to add the word “filtration” in front of it.  Filtration media is really anything that helps filter the water in your tank.  Media is often added to a sump, placed in mesh bags, or added to a reactor.

Media Bags

A mesh bag that can be filled with various types of filtration media and placed into your tank to help filter the water. Less effective than using a reactor.

Media Basket

Usually made of acrylic, a media basket is a removable container, usually placed in a rear filtration chamber, that has several different levels for holding various media such as a sponge filter, bioballs, and activated carbon.

Media Reactor

Any sort of canister that water passes through that allows the media to “react” with the water. Reactors are named based on the media they are designed to hold. Some of the most common in the saltwater aquarium hobby are carbon, GFO, kalkwasser, and calcium.

Carbon/GFO Reactor
Calcium Reactor

Metal Halide Light

The old lighting standard in the hobby, metal hallide lights are high output bulbs that produce a lot of PAR. Popular in the hobby because of their proven track record for coral growth, there are downsides. Metal Halide bulbs require bulky fixtures to reflect the light, they consume comparably high amounts of electricity, and they run quite hot.

Mixed Reef Tank

A mixed reef tank is any saltwater aquarium that houses a mixture of soft corals, SPS corals, and LPS corals.

120 gallon saltwater fish tank with corals and live fish
© My First Fish Tank, 2019

Nano Tank

A small saltwater aquarium. While there is no technical definition, some hobbyists consider anything under 20-40 gallons a nano tank. Although some of these tanks can be less than a gallon!

Waterbox 30 Gallon AIO Saltwater Aquarium


Hobbyist lingo for anemones.


Nitrate is a polyatomic ion (huh?), but also the end result of the nitrogen cycle. For saltwater hobbyists, the presence of high levels of nitrates can mean that the cycle is nearing completion, or that the bioload of the system is too high, meaning there is too much uneaten food or fish waste.


The biological process that turns ammonia into nitrite. A spike in nitrites is an indicator that your tank is cycling.

Nitrifying Bacteria

Tiny organisms that are responsible for converting ammonia into nitrite.


Nitrite is the byproduct of ammonia oxidation (huh?). In the saltwater aquarium, we test for nitrite while our tanks are cycling. During the cycle, ammonia will spike first, followed by nitrite, and then finally nitrate.

Nitrogen Cycle

Also called “the cycle.” In an aquarium, the nitrogen cycle refers to various stages involved with turning ammonia into nitrate. Hobbyists will often say “My tank is cycled”, which means that beneficial bacteria have colonized and decomposing waste is now successfully being transformed from toxic ammonia to nitrates. In a saltwater aquarium, this process usually takes several weeks.

nitrogen cycle infographic
© Marine Depot

Nuisance Algae

Any type of algae that tends to take over a tank, covering rock-work and corals, and being difficult to remove.

For example, diatoms could be considered nuisance algae because they are unsightly, but then again they are somewhat easy to remove and usually show up as a part of your tank cycling.

Two clear examples of nuisance algae in the marine aquarium would be hair algae and bubble algae.  Both these types grow quickly, are not readily eaten by average cleanup crews, and can easily take over an entire aquascape.

There is no hard and fast list of what makes up nuisance algae, but if it’s an algae that’s a pain in your side, you can rightly call it a nuisance!

Nuisance algae can be removed manually, by using certain livestock, by using certain chemical treatments, by reducing phosphates, by installing a refugium, etc.  You get the idea!

The best cure for nuisance algae is prevention.  Properly quarantining your livestock can help you spot problem algae before reaching your display tank.

© Marine Depot
© Marine Depot


Oxidation-Reduction Potential. Hobbyists used to think that ORP measured the cleanliness of water, but the understanding now is closer to this: ORP measures the oxidizing power of the water, meaning the capacity of the water to clean itself. That’s the best I can do, because I really don’t understand ORP!


Either internal or external, are basically a dam inside your tank. They maintain a constant water height in your aquarium, and are usually controlled by gravity. Water “overflows” into the overflow box, and is then transported to your sump for filtration. Overflows are great for removing oils and debris from the water’s surface.


Photosynthetically Active Radiation. PAR is the light range that corals and anemones can use for photosynthesis. Certain corals have certain PAR requirements, and understanding the PAR outputs of your lights is crucial for their health. For example, soft corals require low PAR levels (100ish) and small polyp stony (SPS) corals require high PAR levels of 250-350.

PAR Meter

Measures the amount of PAR (photosynthetically active radiation) from your aquarium lights.


When hobbyists refer to “water parameters”, we are referring to various measurements such as pH, temperature, salinity, ammonia, nitrite, nitrate, phosphate, calcium, alkalinity, etc. Often when trying to get to the root of a problem, the first question a fellow hobbyist will ask is “what are your parameters?”

front view of api saltwater test kit in original packaging

Pellet Food

Any sort of granular fish food. Can be floating or sinking, pellet food is usually concentrated food that comes in various recipes for various types of livestock.

Peristaltic Pump

A peristaltic pump is any pump that uses peristaltic movement to transfer liquid.  Peristalsis is the “radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube” (Wikipedia).

Basically, think of your esophagus, intestines, or colon.  Peristaltic movement is what moves food through your body. In a pump, this is accomplished by a couple rollers that push liquid through the tubing.

Peristaltic pumps are most commonly found as doing pumps, as they are capable of dispensing highly accurate amounts of liquid in small doses.



Stands for “potential of hydrogen”, pH is the measure of the acidity or alkalinity of a solution, with 7 being neutral. Most hobbyists shoot for a range of 8.0-8.4 in their aquariums, but slight variations either higher or lower can be acceptable. It is more important to avoid large swings in pH, rather than a certain number.


A Phosphate is a chemical derivative of phosphoric acid” (Wikipedia). In the saltwater aquarium hobby, phosphate is important because it is food for algae. Oftentimes if your tank has a nuisance algae problem, it is because there are elevated levels of phosphate in your tank.

ultra low range hanna colorometer, green on white background with PO4 reading of 0.5 ppm

Photo Period

The photo period of your tank is the amount of time each day that your lights produce PAR (photosynthetically active radiation). So while your lights may be on for eight hours in a day, your photo period may only be four hours.


A powerhead a small pump that is usually used to create water movement in either your tank, or as a utility pump to mix saltwater. A powerhead can be something simple like a fixed rate ac pump, or it can be a controllable dc wavemaker.

Prazi Pro

Brand name of praziquantel, it is an anti-worm medication used to treat flukes, tapeworms, flatworms, and turbellarians. Commonly used in the saltwater aquarium hobby.


Usually a narrow measuring device that is submerged in water to provide immediate readings of various parameters such as temperature, pH, and ORP.

Protein Skimmer

A type of mechanical filtration, a protein skimmer traps small pieces of organic matter by use of bubbles. A filter sock or sponge will catch the larger pieces of fish and food waste, and the protein skimmer will polish your water by filtering out the smaller particles.

© Marine Depot


Quarantine Tank. A quarantine tank is a separate tank from your main display tank used for quarantining fish and other livestock. A quarantine tank can be any size, but is generally a simple set up with a heater, HOB filter, simple light, and pieces of to allow hiding places for your fish. A quarantine tank is best practice anytime you purchase livestock, as you can add medications into the water and closely monitor your livestock for signs of disease.

Quarantine Tank

A quarantine tank is a separate tank from your main display tank used for quarantining fish and other livestock. A quarantine tank can be any size, but is generally a simple set up with a heater, HOB filter, simple light, and pieces of to allow hiding places for your fish. A quarantine tank is best practice anytime you purchase livestock, as you can add medications into the water and closely monitor your livestock for signs of disease.