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Vocab & Jargon D-K

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In a saltwater aquarium, detritus refers to fish waste or uneaten food that usually settles at the bottom of the tank. Excess detritus can lead to ammonia and phosphate spikes.


A group of brown colored microalgae that is commonly found in saltwater aquariums. Diatoms appear in almost every saltwater aquarium at some point, usually soon after or during the cycling process. While not dangerous, they are unsightly but as long as you have good filtration and flow, they will usually go away on their own in a matter of days or weeks.

Dinos / Dinoflagellates

Often dreaded in the saltwater aquarium, there are over 1,500 species that we know of. Dinos are protists, meaning they are neither a fungus, plant, or animal.

If you live near the coast you may have heard of a “red tide” which makes it dangerous to eat shellfish. This is caused by a type of dinoflagellate.

Under a microscope, dinos have a vastly different structure from algae. Dinos are usually reddish in color, and as they grow, look like a thick mucus that often has air bubbles attached the end.

Dinos are dreaded by hobbyists because they are toxic to your livestock. Grazing snails, crab, and algae eating fish who ingest dinos will likely die.

Dinos are also tricky to get rid of in a marine aquarium. Dino’s probably exist to some extent in most aquariums, but when something gets out of whack, they can bloom and quickly take over. One cool thing about dinos in the ocean, they are the protists that are responsible for bioluminescence.

Display Tank

The portion of your aquarium that is easily visible and separate from either your sump, HOB filter, or rear filtration chamber.

picture of 120 gallon aquarium on grey stand with led lights hanging over it
© My First Fish Tank, 2019

Distilled Water

Highly purified water that can be used in saltwater aquariums. Distilled water is created by heating water until it becomes vaporized, and then condensing the vapor back into water in a separate location.

Dosing Pump

A peristaltic pump which is usually used to slowly add calcium, alkalinity (soda ash), and magnesium to an aquarium. Good for dosing because of the slow speed and ability to add a few drops at a time.

Drip Acclimation

Drip acclimation is the process of slowly equalizing the water parameters from the fish store to your aquarium. Usually done by putting your new livestock in a bucket and starting a siphon with a portion of airline tubing. Then, over the span of 30 minutes, water from your tank is slowly added to the LFS water, equalizing water parameters such as temperature and pH, thus reducing stress in your fish.

Drip Loop

A loop in your electrical wire that goes down below the outlet and then back up to the outlet. It protects your outlet from water that may run down the wire by accident.

© Marine Depot

Drip Plate

Usually a piece of acrylic with many holes drilled through it, allowing water to be evenly distributed as it reaches the sump.

Dry Live Rock

Live rock, either human-made, mined, or pulled from the ocean, that is dried out before shipping. Helps to kill off unwanted hitchhikers, but will also not have any beneficial bacteria when it arrives. It is technically not “live” when it arrives at your home, but after the cycle is complete, it will become “live” rock.

Durso Standpipe

A Durso Standpipe is used in a weir to make your overflow silent. It looks like a piece of pvc pipe attached to a tee which is attached to an elbow.


Epoxy is used in the aquarium hobby for a couple reasons. To attach coral to an aquascape and to attach pieces of live rock together. You can purchase an aquarium safe putty in various colors to match your aquascape. While smelly, it is reef safe and cure under water. Epoxy for aquariums comes in long tubes of putty that have to be mashed together to activate.

External Pump

Any type of pump that that can be placed outside of the water.  Some submersible pumps have the ability to also be external pumps.

Filter Feeder

Any type of livestock that consumes food by filtering out of the water column. Clams, Feather Duster Worms, and Sea Cucumbers are a few examples. These types of animals help keep your water clean.

Filter Floss

Filter floss is hobbyist lingo for any type of polyester fiber, usually used as a stuffing for various sewing projects.  It is popular because it is extremely inexpensive, disposable, and easy to replace.  A lot of hobbyists use filter floss instead of a sponge, because it is more convenient to just replace the floss every few days than having to rinse out the sponge.

Filter Media

Filter media refers to anything that is placed in a filter that helps remove something undeseriable from the water. For example, activated carbon, GFO, and biopellets.

Filter Pad

Refers to anything from a simple sponge to a multi-layered pad with varying levels of mechanical and chemical filtration. A popular example of a filter pad is either a black sponge or a Poly-Filter

Filter Sock

A filter sock is used to mechanically filter aquarium water. It comes in a couple different materials and mesh sizes, but generally speaking it is made of felt. It looks like a white sock attached to a plastic ring. A filter sock is used to catch large pieces of organic matter that can then be manually removed before breaking down into ammonia.

Flake Food

Any type of dry fish food that comes in thin layers.


A fish behavior of quickly rubbing against a rock or other hard surface.  It almost looks like the fish has an itch.  It is often a symptom of a disease as the fish is trying to remove it from its body.

Flexible Tubing

Usually made of vinyl or silicone, flexible tubing is used throughout the aquarium hobby.  It is used with utility pumps, it attaches to return pumps, it can also run reactors and attach to bulkheads as your drain.

Basically, it is the opposite of a hard plumbed system which uses pvc.  

Flexible tubing is easy to use, inexpensive, and usually attaches to hose barbs by means of a plastic hose clamps.

Float Switch

A float switch is used to detect the water level and turn on/off some sort of equipment. These are most often used in an auto top off system or when making RO/D/I water. A float switch is basically a piece of plastic that is filled with air that floats in the water. So as the water level gets high, it can either trigger a mechanical sensor, or just mechanically force a valve shut.


Formalin is a mixture of formaldehyde and methyl alcohol. It is primarily used to treat Brooklynella, a disease common to clownfish.


Fish Only With Live Rock. A FOWLR system uses live rock as the primary biological filter, and only has fish and invertebrates as livestock. A reef tank would have fish and coral.


A frag is a small piece of coral that was either intentionally removed or broken/cut away from a larger colony.  Popular in the hobby because frags are much cheaper than entire colonies.

Frag Plug

A small ceramic disk used to attach a frag to.

Frag Rack

A plastic rack used for holding frag plugs

Frozen Food

Comes in all shapes and sizes, there is frozen food specifically designed for all types of fish, filter feeders, anemones, and corals.


Granular ferric oxide. Used to remove excess phosphate from the water.

brown gfo pellets in clear plastic bottle

Glass Lid

A glass covering placed over an aquarium to reduce evaporation and protect jumping fish.

Gravel Vacuum

A large plastic tube attached to a hose. Used to siphon water from your tank during water changes, as well as cleaning detritus from your sandbed.

Siphon gravel vacuum in original packaging

GSP Garden

Green Star Polyp Garden. Green Star Polyps are an easy to keep soft coral that grow quickly over your aquascape. Because it can grow quickly, you have to be careful where you put it or it can take over your tank. Many hobbyists have started doing “GSP Gardens” to limit the boundaries of where the GSP can grow. Usually a small piece of GSP is attached to a small piece of rock that is then placed away from the main aquascape to create an island. This way, as the GSP grows, it will look like a beautiful green garden island, but will be easy to maintain and trim back away from the glass and main aquascape.

By PilarMeca - Own work, CC BY-SA 3.0,

Hang On The Back Filter

Any sort of filter that hangs on the side of your tank.

Hard Coral

Also called stony corals (as opposed to soft corals), hardcorals are any coral that build a hard calcium carbonate skeleton.  All tropical reefs are made by hardcorals.

Most hobbyists break up hard corals into two distinct categories: LPS (Large Polyp Stony) and SPS (Small Polyp Stony), based on the overall size of the polyps.

LPS Coral © My First Fish Tank
SPS Coral By RevolverOcelot - Own work, CC BY-SA 3.0,

Hard Plumbing

Refers to an aquarium that uses PVC piping instead of flexible tubing to transport water between the display tank and the filtration equipment (usually a sump).

© My First Fish Tank, 2019

Herbie Style

A silent overflow method, a Herbie Style overflow system uses both a primary and emergency drain pipe. A ball or gate valve is attached to the primary pipe, and the emergency pipe is several inches taller. By adjusting the valve, you can tune a Herbie Style overflow so that the water in the weir sits just above the primary drain but below the emergency drain, thus making it virtually silent.

Herbie Style Overflow Diagram


In the saltwater aquarium hobby, hitchhikers refer to any organism that “catches a free ride” on something else.  Most commonly, hitchhikers find their way into your aquarium by attaching to corals, inverts, fish, or live rock.

Some hitchhikers can be beneficial to your aquarium.  Certain worms can eat detritus and and snails can help keep your glass clean.

But some hitchhikers are a nuisance. 

Hitchhikers include the following plus tons more: shrimp, worms, crabs, snails, aptasia, and starfish.

It is always best practice to use a quarantine tank and carefully inspect and remove any visible hitchhikers before adding them to your display tank.

By User:Haplochromis - Self-photographed, CC BY-SA 3.0,
By Neıl ☎ - self-made, CC BY-SA 3.0,

HOB Filter

Hang On the Back filter. Any sort of filter that hangs on the side of your tank.

Hospital Tank

Another type of quarantine tank, a hospital tank is usually used to treat emergency fish diseases. It is a simple glass tank with only a heater, mechanical filter, and pieces of pvc to allow hiding spots for fish. Some hobbyists leave their hospital tanks up all the time, while others will break it down in between uses.

Hybrid Lighting

Refers to any type of aquarium lighting that blends more than one fixture. For example LED and T5 is a common hybrid lighting system.


A simple plastic instrument that measure the relative density of a liquid. For the aquarium hobby, it measures how much salt is in your water.

coralife hydrometer in manufacterers packaging

Ich (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


An animal that doesn’t have a backbone. In the saltwater hobby, these are most often snails, crabs, starfish, mollusks, worms, etc.


German for “lime water”, kalkwasser is often used as a single source of adding calcium and alkalinity to your saltwater. Can be manually dosed, used in a reactor, or added to a dosing pump. Kalkwasser does raise pH, so it cannot be used to increase calcium in your tank, but rather to hold levels steady.