Aquarium Glossary
Terms and definitions covering saltwater, freshwater, coral, and invertebrate care — everything you need to shop and care for your tank with confidence.
General
Acclimation
The process of gradually adjusting a newly purchased fish, coral, or invertebrate to your tank's water conditions before release, reducing shock and stress from differences in temperature or chemistry.
Aquascape
The overall visual layout of a tank's interior, including how rock, substrate, plants, and decor are arranged to create a natural or designed look.
Bioload
The total amount of waste that a tank's livestock produces, which determines how much filtration and how many water changes the system needs to stay healthy.
Community Tank
A tank stocked with multiple species chosen for compatible temperaments and similar water needs, allowing them to coexist peacefully.
Cycling
The process of establishing a healthy population of beneficial bacteria in a new tank before adding livestock, so ammonia and nitrite are processed safely from day one.
Detritus
Dead organic material and waste, such as uneaten food and decaying matter, that accumulates in an aquarium and is broken down by bacteria and cleanup crew members.
DOA
Short for "Dead on Arrival," a livestock shipment that arrives dead or in critical condition. Most reputable shippers and local stores offer a guarantee or replacement policy for DOA arrivals, usually requiring a photo or report within a set window after delivery.
Drip Acclimation
A slower, more precise acclimation method that introduces tank water into a new arrival's container at a controlled drip rate over 30-60+ minutes, used for sensitive or high-value livestock.
Float Acclimation
A quick acclimation method where the sealed bag containing a new arrival is floated in the tank for 15-20 minutes to equalize temperature before the animal is released.
Saltwater
Aiptasia
A fast-spreading pest anemone that can hitchhike into a saltwater tank on live rock or coral. Aiptasia stings neighboring corals and reproduces rapidly, making early removal important — commonly controlled with a Peppermint Shrimp, targeted dosing treatments, or manual removal.
Aragonite
A calcium-based mineral commonly used as marine substrate, which helps buffer pH and adds mineral hardness to saltwater systems.
Coralline Algae
A beneficial pink or purple encrusting algae that grows on rock and glass in healthy reef tanks, generally seen as a sign of good, stable water conditions.
FOWLR
Short for Fish Only With Live Rock, a saltwater setup that includes fish and live rock for filtration and aesthetics, but no corals.
Live Rock
Porous rock from a marine environment that hosts beneficial bacteria and small organisms, used in saltwater tanks for both biological filtration and natural-looking aquascaping.
Freshwater
Biotope Aquarium
A tank designed to closely replicate the specific natural habitat of its inhabitants, from substrate and decor down to water chemistry, rather than a mixed or decorative setup.
Black Beard Algae
Often called BBA, a dark, bristly nuisance algae that clings stubbornly to plants, decor, and slow-moving surfaces, generally signaling a nutrient or flow imbalance in the tank.
Blackwater
Dark, tannin-stained water created by decaying leaves, wood, or other botanicals, mimicking habitats like the Amazon basin and often preferred by species such as certain tetras and killifish.
Brackish
Water with a mild salt content, falling between freshwater and full-strength saltwater, found naturally where rivers meet the sea and used for species like mollies and certain gobies.
Bubble Nest
A floating cluster of air bubbles built by male bettas and gouramis to hold and protect their eggs after spawning.
Fry
Newly hatched or newly born baby fish, which typically require finer food and extra protection from adult tankmates until large enough to fend for themselves.
Live-Bearer
A fish that gives birth to free-swimming live young rather than laying eggs, such as guppies, platies, and mollies, popular with beginners for their easy breeding.
Coral
Actinic Lighting
Blue-spectrum aquarium lighting that supports photosynthesis in corals and other reef organisms while producing the vivid fluorescent look many reef keepers favor.
Allelopathy
A form of chemical warfare between corals, where certain species release compounds into the water to inhibit or damage the growth of nearby competing corals.
Coral Dipping
Treating a new coral with a specialized dip solution before adding it to a display tank, to remove hitchhiking pests such as flatworms or red bugs.
Frag
A cutting or fragment of coral taken from a larger colony and grown out as its own new colony, the primary way corals are propagated and sold.
Frag Plug
A small ceramic or resin disc that a coral cutting is attached to while it heals and grows, giving it a stable base until it can be mounted permanently in a display.
Fragging
The act of cutting a piece from a coral colony to propagate a new, genetically identical colony, commonly used by hobbyists and shops to grow and trade coral.
Invertebrate
Amano Shrimp
A large, hardy freshwater algae-eating shrimp popular for keeping planted tanks clean, known for rarely breeding successfully in home aquariums due to a larval saltwater stage.
Caridina
A genus of freshwater shrimp, including Crystal and Bee shrimp varieties, that generally requires more precise, soft water chemistry than hardier Neocaridina species.
Cleaner Shrimp
A marine shrimp, such as the scarlet skunk cleaner, that sets up a cleaning station where fish visit to have parasites and dead tissue picked off, a natural symbiotic behavior.
Cleanup Crew
A group of invertebrates such as snails, hermit crabs, and shrimp added to a tank to consume algae, leftover food, and detritus, helping keep the system clean naturally.
Copper Sensitivity
A trait of most invertebrates, including shrimp, snails, and corals, that makes them lethally sensitive to even trace amounts of copper from medications, fertilizers, or old plumbing.
Emerald Crab
A reef-safe crab popular in cleanup crews for its appetite for bubble algae, a nuisance algae many other cleanup species tend to avoid.
Equipment
ATO
Short for auto top-off, a device that automatically replenishes water lost to evaporation, helping keep salinity stable in reef and marine tanks.
Biological Filtration
Filtration powered by beneficial bacteria that break down ammonia into nitrite and then nitrate. This is the core filtration process keeping an aquarium safe for livestock.
Canister Filter
A large-capacity external filter connected by tubing, offering strong mechanical, biological, and chemical filtration, popular for larger freshwater tanks.
Chemical Filtration
Filtration that removes dissolved substances from water using specialized media, such as activated carbon, to pull out odors, discoloration, and certain toxins.
CO2 System
Equipment that introduces dissolved carbon dioxide into a planted freshwater tank to fuel photosynthesis and encourage lush, faster plant growth.
Dechlorinator
A water conditioner product that neutralizes chlorine and chloramine in tap water, making it safe to add to an aquarium.
HOB Filter
Short for hang-on-back filter, an external filter that clips onto the rim of the tank, popular in beginner freshwater setups for its simplicity and easy maintenance.
Water Chemistry
Alkalinity
Also called dKH, a measure of water's buffering capacity, or its resistance to sudden pH swings. Reef tanks generally target 8-12 dKH, and this value directly fuels coral skeleton growth.
Ammonia
A toxic compound produced by fish waste, uneaten food, and decaying organic matter. It is the first and most dangerous stage of the nitrogen cycle and must be broken down by beneficial bacteria before it harms livestock.
Calcium
An essential mineral corals use to build their stony skeletons. Reef tanks are typically kept between roughly 380-450 ppm to support steady coral growth.
Carbon Dosing
Adding an organic carbon source, such as vinegar, vodka, or a commercial dosing product, to a reef tank to fuel bacteria that consume dissolved nitrate and phosphate. The bacteria are then exported from the system by a protein skimmer. Dosing typically starts at a low volume and increases gradually to avoid crashing oxygen levels.
GH
Short for General Hardness, a measure of the overall concentration of dissolved minerals like calcium and magnesium in freshwater, important for fish and plant health, and critical for freshwater shrimp.
Kalkwasser
Also called limewater, a saturated calcium hydroxide solution slowly dripped into a reef tank to help raise and maintain calcium and alkalinity levels.
KH
Short for Carbonate Hardness, a measure of the water's buffering capacity that helps keep pH from swinging suddenly, especially important in planted and shrimp tanks.
Health & Disease
Bleaching
The loss of a coral's color, caused when it expels its symbiotic algae in response to stress such as excess light, poor water quality, or high temperature. A bleached coral is still alive but at serious risk.
Failed Molt
Sometimes called the white ring of death, a fatal molting failure where a shrimp becomes stuck in its old exoskeleton, most often caused by insufficient GH or calcium in the water.
Ich
A common parasitic disease that appears as small white spots resembling grains of salt across a fish's body and fins, usually triggered by stress or a rapid environmental change.