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Vocab & Jargon R-Z

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Rose Bubble Tip Anemone

Rose Bubble Tip Anemone top down view


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

Rear Filtration

There are three primary ways saltwater aquariums filter water: By using a “hang on the back“, by use of a sump, or by use of a rear filtration chamber. A rear filtration chamber is merely a rectangular section of your display tank that is partitioned off into an overflow where you can place various types of filters.

Reef Safe

Usually a term used with medications, the term “reef safe” means that it will not have a negative effect on your invertebrates such as corals, shrimp, snails, and crabs.

Many medications on the market are not tolerated by inverts, so if you plan on treating a sick fish in your display tank, it is important to make sure the medication is reef safe.

Reef Tank

A reef tank is a saltwater aquarium that houses corals. The opposite would be a fish only tank. It is important to decide early on whether or not you want a reef tank, because there are many types of fish and invertebrates that are not “reef safe”, meaning they will eat the corals.

Waterbox 30 Gallon AIO Saltwater Aquarium


An instrument that using refraction to measure the salinity of saltwater. Considered to be more accurate than a hydrometer.


A refugium is literally means ” refuge”. In the saltwater aquarium hobby, a refugium is either a hang-on-the-back or a separate compartment in a sump where macro algae is grown to reduce phosphates in the water column, but also to allow the safe breeding of various types of pods (copepods, amphipods, tiger pods), which act as live food for various fish.


Most commonly used for RO/DI water, a reservoir is a container that holds a solution that needs to be added to the tank. Can also be used to house various additives as well as 2-part dosing solutions.

ATO Reservoir
Dosing Reservoir

Return Pump

Any type of AC or DC pump that is used to return water from your filtration chamber to your display tank.

black and grey small return pump with suction feet on white background
AC Return Pump
DC Return Pump


A rimless style tank is any aquarium that does not have anything holding it together except the silicone seams.  For example, a lot of inexpensive tanks that you find at a big box pet store carry simple glass aquariums with a black plastic rim around the edge.  

Or, larger systems sometimes have a “Euro Brace”, which is an interior glass frame that is siliconed to the tank to help provide extra support against the force of the water pushing out against the glass.

© My First Fish Tank

RO Water

Reverse Osmosis Water. Commonly found in home water purifying systems, RO water is filtered by use of a RO membrane. Pressurized water is forced through the semi-permeable membrane, allowing water through and flushing away contaminants. In the saltwater aquarium hobby, RO water by itself is usually not pure enough, which is we RO water is then passed through DI resin to achieve ultimate purity. But beware, while RO water is safe to drink, RO/DI water may actually be too pure and could suck nutrients out of your body.

RO/DI Filter

Reverse Osmosis / De-Ionization Filter. RO/DI filters use various stages and types of filtration to achieve 0 TDS water. Water first passes through a sediment filter, then a carbon filter, then the RO membrane, and finally through de-ionization resin. Considered the gold standard for creating clean water for your saltwater aquarium, the various types of media do have to be replaced depending on the amount of water you make and the makeup of your local water supply.

RO/DI Water

RO/DI water is water that has passed through both a RO (reverse osmosis) membrane and DI (deionization) resin.  The result is ultra-clean water with 0 tds (total dissolved solids).

Warning: Some studies have shown that drinking RO/DI water may actually be bad for you.  The water is so clean that it can dehydrate you and suck necessary nutrients from your body.  I’m no scientist, so do you research.

RO/DI water is the preferred water for use in replacing evaporated water and mixing fresh saltwater for your marine aquarium.


The measure of the amount of salt dissolved in water. The salinity of natural seawater is 3.5%, or 35 parts per thousand.


Short for aquascape. Just like we landscape a yard, we aquascape an aquarium. An aquascape is usually comprised of various pieces of live rock put together in such a way as to provide adequate housing for fish and corals.

70 gallon aquarium with purple rocks and no water
© My First Fish Tank, 2019

Schedule 40/80 PVC Pipe

Schedule 40 refers to the thickness of PVC pipe. The higher the schedule the thicker the pipe. Schedule 40 is the most common schedule, and is easily found at any local hardware store. Schedule 40 is almost always white, and works well for home aquariums.

Schedule 80 is a dark grey color, more difficult to find, and more expensive. Hobbyists will often use schedule 80 PVC, merely because the dark grey color is more pleasing to took at that the white schedule 40.

Schedule 40 Union
Schedule 80 Ball Valve

Screen Top

Any sort of mesh screen lid that attaches or sits on top of your display tank to protect your livestock from crawling or jumping out. Many species of fish jump, so having a screen top or glass lid is important.

Sediment Filter

Any sort of mechanical filter that removes sediment from the water. Sediment filters are most commonly used in the first stage of an RO/DI filter and remove small particulates from tap water.

Silent Overflow

Most saltwater aquariums use one of two methods for getting the water from the display tank to the filter: Either a Hang On The Back (HOB) style pump or some sort of overflow box.

Some sort of overflow is the preferred filtration method, because the surface of any aquarium can become clogged with various oils and fats, as well as household dust and floating fish food.

An overflow uses gravity to push the top surface of water over the edge and into the filtration chamber.  That way all of the oils and debris that are floating on the surface can cascade over and be filtered out.

But, as we all know, when water overflows (think waterfall), it can be noisy for two reasons.  First is the distance between the display tank water height and the height of the water in the overflow box.  There can be a constant loud crashing sound just like a waterfall.

Second, in systems with sumps, water is transported to the sump via pvc pipe, which can create a loud sucking sound caused by the siphon.

A silent overflow solves both of these problems by a) minimizing the distance between the height of the water in the display tank and the filtration chamber and b) using either the Herbie method, Durso Standpipe method, or Bean Animal method to silence the sucking sound made by the siphon.

Phew, that was a long one. Click on the pictures below to learn more about each style!

Durso Standpipe © Marine Depot
Herbie Style Overflow Diagram
Herbie Style © Marine Depot
infographic of bean animal style filtration system
Bean Animal © Marine Depot


Both a noun and a verb, a siphon is any sort of tube that takes liquid from a higher container to a lower container by means of gravity. Most commonly, we use a gravel vacuum as a siphon during water changes to remove detritus from our display tanks.

Gravel Vacuum


Skimmate is the end product of a protein skimmer.  It is usually dark brown in color, and smells terrible!  Skimmate can vary in color depending on whether you run your protein skimmer more on the wet side or dry side.  

A “wet” skimmate would be a lighter brown color because the protein skimmer is tuned to allow more bubbles to overflow into the collection cup.

A “dry” skimmate would be more highly concentrated protein because your protein skimmer was tuned to allow fewer bubbles to overflow into the collection cup.

In essence, skimmate is protein (fish poop, decaying matter, food) that is filtered out of your water column.

© My First Fish Tank

Soft Coral

As opposed to hard coral, soft coral is any coral that does not secrete a calcium carbonate skeleton.

Green Star Polyps © My First Fish Tank
Green Toadstool © My First Fish Tank

Soft Plumbing

Any sort of aquarium plumbing that uses flexible tubing as opposed to PVC.


Hobbyist lingo for soft corals. Soft corals do not secrete a calcium carbonate shell.

Green Star Polyps © My First Fish Tank
Green Toadstool © My First Fish Tank

Specific Gravity

In the saltwater aquarium hobby, we use specific gravity interchangeably with salinity, since both are telling us how much salt is in our water. Whereas salinity is the measurement of salt in water, specific gravity “is the ratio of the density of a substance to the density of a reference substance” (Wikipedia).

Coralife Energy Savers Deep Six Hydrometer


Small Polyp Stony Corals. SPS corals are usually more difficult to keep alive, and require higher amounts of PAR. SPS corals have very small polyps that reside on a stony skeleton, whereas lps (large polyp stony) corals have long, flowing polyps.

Starphire Glass

A brand name for a type of low-iron glass, often considered to be the benchmark glass for clarity. Starphire glass is noticeably clearer than regular glass. Starphire uses low-iron silica which drastically reduces the blue/green tint in most glass.

© My First Fish Tank

Stony Coral

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

Most hobbyists break up stony 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,

Submersible Pump

Any type of AC or DC pump that can be submersed in water. Most often these are return pumps, utility pumps, and wavemakers.

black and grey small return pump with suction feet on white background
AC Return Pump
DC Return Pump


Usually sand, rock, or crushed coral that sits at the bottom of your aquarium. Substrates are important for various kinds of livestock that need it for survival.

wet live sand for saltwater aquariums


In saltwater aquariums, a sump is an acrylic or glass container with partitions and baffles, usually located directly below the display tank, suited for hiding equipment and filtering water.

T5 Light

T5 (Tubular 5/8 inch) fluorescent lights are slim fluorescent fixtures and bulbs that are popular as supplemental lighting in saltwater aquariums. T5 light bulbs are commonly used conjunction with LED fixtures to provide a wide spread of actinic lighting.

Target Feeding

A method of feeding corals and other invertebrates that uses some sort of syringe or baster to deliver food directly to the animal.  The opposite of this would would be broadcast feeding, whereby you dump food into the tank and let the current carry it to the invertebrates.

TDS Meter

A small device used to measure the concentration of total dissolved solids in water. Used when making RO/DI water.

TDS Meter Water Quality Tester

Test Kit

Any sort of equipment used to test for things in water. Some of the most common in the saltwater aquarium hobby are the following: Ammonia, nitrite, nitrate, phosphate, calcium, alkalinity, magnesium, and pH.

front view of api saltwater test kit in original packaging

Tiger Pods

Slightly larger than your standard copepod, these pods are popular live foods for your fish and corals.

By Aidan Long - Own work, CC BY-SA 4.0,

Trace Elements

Trace elements are the components of saltwater that make up less than .01%. They make up a very small percentage of your saltwater, but may be important for coral health and growth. Most hobbyists rely on water changes to replenish trace elements, but you can also dose trace elements.

Trickle Filter

Uncommon in the saltwater hobby, a trickle filter uses gravity to allow water to “trickle” through various stages of filtration before being returned to the display tank.  Often called a Wet/Dry Trickle Filter

Two Part Dosing

Often quite confusing, two-part refers to calcium and alkalinity, but no two-part dosing is complete without a third part… magnesium.

You dose the calcium and alkalinity in equal parts since they are usually consumed at the same rate by corals and invertebrates. Magnesium is usually added in much smaller quantities. In a fish only system, or a lightly stocked reef tank, weekly water changes will usually be enough to replace the calcium and alkalinity. But if you have a system with lots of corals, two part dosing becomes necessary for coral growth.

two 1 liter white jugs side by side on white background

Utility Pump

The exact definition in the aquarium hobby is sort of a moving target, but basically it is this:

A small, submersible powerhead that is often used to mix saltwater, pump RO/DI water, or as extra flow in your tank.

Basically, a utility pump is used for maintenance tasks and is usually not turned on all the time.

For example, I use utility pumps to mix my saltwater, to move my RO/DI water between containers, as a powerhead in my quarantine tank, and to assist in water changes.

UV Sterilizer

A type of filter that utilizes ultraviolet lights to kill free floating microorganisms that can cause fish disease and unwanted algae growth. Water is pumped into a PVC pipe which contains the uv light, and then passes through and returns to the tank. Only free floating microorganisms are effected as they need to be pulled into the filter in order to pass by the uv light.


Usually referred to as a gravel vacuum or siphon, this simple plastic device is used for removing detritus from your substrate. Usually a hobbyist controls the flow by pinching the flexible tubing to make sure that the sand or gravel does not get removed along with the detritus.

Gravel Vacuum

Water Change

The process or removing a certain percentage of water from your aquarium and replacing it with fresh saltwater. Usually considered a weekly chore, water changes help remove detritus and replace minor and trace elements necessary for coral growth.

Water Column

Simply put, the water column consists of all the water between your substrate and the surface.  

Scuba divers use the term “water column” to refer to the water in which they dive, and scientists break up the water column of the ocean by depth.


Usually a DC powerhead that creates varied flow inside of your tank to mimic the water movement in the ocean. Can be a simple AC pump that turns on and off by use of a controller, or a fancy DC pump with virtual unlimited programability.


A dam that sits in the back of your tank that separates the filtration/plumbing from your display.

Wet/Dry Filter

Not common in the saltwater hobby, a wet/dry filter usually uses bioballs that sit above the water line. Water is passed over and through the bioballs before entering the sump and returning to the display tank. The thought is that by keeping the bio media above the water line, the amount of oxygen is increased thus aiding the density and amount of healthy bacteria to filter your water.

White Spot Disease

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