Aquarium & Aquascaping Glossary
Plain-English definitions for the words and abbreviations you'll run into around the club, on this site, and in the wider hobby — no assumed knowledge required.
Every hobby has its own shorthand, and fishkeeping has more than most. If you've hit a term on one of our care guides, in a forum post, or from another member at a meeting and drawn a blank, this page is for you. New to it all? Our Beginner's Roadmap walks through the whole process in order — this glossary is here for whenever you need to look something up along the way.
Club Shorthand
ECAAC's own acronyms
These four come up constantly around the club — they're our award programs, and each has its own page and downloadable guide.
BAP
Breeding Awards Program — recognises members for breeding fish, invertebrates and amphibians.
HAP
Horticulture Awards Program — recognises members for propagating aquatic plants.
AAP
Aquascaping Awards Program — recognises members for planted and hardscape layouts.
SBP
Specialist Breeder Program — recognises members who breed extensively within one fish category.
A
- Acclimation
- Slowly adjusting a new fish or plant to your tank's water temperature and chemistry before releasing it, usually by floating the bag and/or drip-acclimating over 20–60 minutes. Reduces shock and stress on introduction.
- Aquascape
- An underwater layout built with hardscape (rock, wood) and plants, arranged with the same design intent as a garden or landscape photograph. See our Art of Aquascaping guide.
- Ammonia (NH₃/NH₄⁺)
- The first, most toxic waste product fish produce, also released as plant matter and uneaten food decay. A healthy, cycled tank converts it to nitrite almost immediately. See the nitrogen cycle.
- Anubias
- A hardy, slow-growing rhizome plant that attaches to wood or rock rather than being planted in substrate — a common beginner-friendly aquascape plant.
B
- Bioload
- The total waste-producing "load" your livestock places on a tank's filtration — more or larger fish, more waste, more demand on your filter and water changes.
- Biotope
- An aquarium set up to recreate a real wild habitat as closely as possible — matching the water, hardscape and species to an actual place, like Lake Malawi or a Southeast Asian blackwater stream. Try our Biotope Wizard.
- Blackwater
- Tannin-stained water, typically soft and acidic, coloured by decaying leaves and wood — found in habitats like the Amazon and used deliberately in some biotope tanks. See Blackwater Aquariums.
- Brackish
- Water with salinity between fresh and full marine, found where rivers meet the sea. A smaller niche within the hobby, home to species like archerfish and some gobies.
- Bristlenose (BN)
- A common, hardy algae-eating catfish (genus Ancistrus) popular for both community tanks and easy breeding.
C
- Canister filter
- An external filter housed in a sealed canister outside the tank, connected by hoses — larger capacity and quieter than most internal filters. See Filter Types Explained.
- Cichlid
- A huge, diverse family of freshwater fish, many known for parental care and territorial behaviour — includes Malawi mbuna, Tanganyikan species, and South American dwarf cichlids.
- CO₂ injection
- Adding carbon dioxide to a planted tank to accelerate plant growth, usually via a pressurised cylinder and regulator. See CO2 Systems Explained.
- Community tank
- A tank stocked with multiple peaceful species chosen to get along, as opposed to a species-only or biotope tank.
- Crypt melt
- The sudden, alarming die-back Cryptocoryne plants show after being moved or after a change in water conditions — usually temporary, with new growth returning once the plant adjusts.
- Cycling
- Establishing the colony of beneficial bacteria that converts ammonia to nitrite to nitrate before adding fish. See the nitrogen cycle guide.
D
- Dither fish
- Confident, active fish added alongside shy or territorial species to signal "it's safe" and encourage natural behaviour — common in cichlid setups.
- Driftwood
- Wood used as hardscape and, for some species, a grazing surface — often pre-soaked or boiled to sink it and reduce tannin release.
- Drop checker
- A small glass device that uses a colour-changing reagent to show CO₂ levels in a planted tank at a glance — green is the usual target. See CO2 Systems Explained.
- Dutch style
- An aquascaping style built from dense rows and terraces of contrasting plants, with little to no hardscape — the opposite approach to Iwagumi. See The Art of Aquascaping.
E
- Emersed growth
- A plant grown with its leaves above the waterline rather than fully submerged — often how aquatic plants are propagated commercially, since it's faster and easier than underwater growth.
- EI dosing
- "Estimative Index" — a fertiliser dosing method for planted tanks that deliberately overshoots nutrients slightly, relying on regular water changes to reset levels rather than precise measurement.
F
- Fishless cycling
- Cycling a new tank using pure ammonia (or fish food/shrimp to decay) instead of live fish, so no animal is exposed to the toxic ammonia and nitrite spikes. See the nitrogen cycle guide.
- Flare
- A betta displaying by extending its gill covers and spreading its fins, usually in response to a rival, mirror, or another betta — a normal, healthy behaviour in short bursts. See Betta Fish Care.
- Fry
- Newly hatched or newborn fish, before they're big enough to be called juveniles.
G
- GH (General Hardness)
- A measure of dissolved calcium and magnesium in water — "hard" water has more, "soft" water has less. Matters a lot for breeding and for species from soft-water habitats. See Water Quality.
- Gravel vacuum
- A siphon tool used during water changes to pull debris out of the substrate while draining old water — standard maintenance kit for most tanks.
H
- Hardscape
- The non-living structural material in an aquascape — rock and driftwood — arranged before planting to set the layout's composition.
- Hillstream
- A fast-flowing, highly oxygenated stream habitat, home to specialised fish like hillstream loaches that cling to rocks in current. See Southeast Asian Biotope.
- HOB filter
- "Hang-on-back" — a filter that clips onto the back rim of the tank, drawing water up and returning it via a waterfall-style outflow. See Filter Types Explained.
I
- Ich (white spot)
- A common parasitic disease showing as small white spots across the body and fins — treatable, but needs prompt action. See Fish Disease Identification & Treatment.
- Immersed / submersed
- "Immersed" (or emersed) means grown above water; "submersed" means fully underwater — the same aquatic plant can often be grown either way, with different leaf shapes as a result.
- Invertebrate
- Any animal without a backbone kept in the hobby — shrimp, snails, crabs and crayfish are the most common in freshwater tanks. See Invertebrates for Freshwater Tanks.
- Iwagumi
- A minimalist Japanese aquascaping style built around an odd number of carefully placed stones and low-growing carpet plants, with no fish centrepiece. See Iwagumi Aquascaping.
J
- Jungle style
- A deliberately dense, overgrown aquascaping style that embraces plants left to grow wild rather than trimmed into tidy shapes. See The Art of Aquascaping.
K
- KH (Carbonate Hardness)
- A measure of water's buffering capacity against pH swings — low KH water can crash in pH unexpectedly, so it's one of the first things worth testing. See Water Quality.
- Killifish
- A large group of small, often brilliantly coloured fish; several African species are annuals whose eggs survive their habitat drying out completely. See African Killifish.
L
- LFS
- "Local Fish Store" — hobby shorthand for a bricks-and-mortar aquarium shop, as opposed to ordering online.
- Livebearer
- A fish that gives birth to free-swimming fry rather than laying eggs — guppies, platies and mollies are the classic beginner examples.
- LFS-safe / QT
- See Quarantine tank below — new stock is usually held separately before joining an established tank.
M
- Mbuna
- A group of rock-dwelling Lake Malawi cichlids, known for bold colours and territorial behaviour — among the most popular African cichlids in the hobby. See Lake Malawi Aquariums.
- Morph
- A distinct colour or pattern variant within a species, often selectively bred — used constantly around shrimp (see Neocaridina/Caridina morphs) and Medaka.
N
- Nano tank
- A small aquarium, generally under 40 litres — its small water volume means water quality can swing fast, so stocking and maintenance need extra care. See Nano Aquarium Setup Guide.
- Nature style
- An aquascaping style inspired by natural landscapes — mountains, forests, valleys — using asymmetric hardscape and a mix of plant textures. See The Art of Aquascaping.
- Nitrite (NO₂⁻)
- The second, still-toxic stage of the nitrogen cycle, produced when bacteria break down ammonia. Converted to the far less harmful nitrate by a second bacteria colony. See the nitrogen cycle guide.
- Nitrate (NO₃⁻)
- The end product of the nitrogen cycle — much less toxic than ammonia or nitrite, but still needs managing through water changes and/or plants, since it builds up over time.
O
- Osmosis / RO water
- "Reverse osmosis" — a filtration process that strips water down to near-pure H₂O, used to create very soft water from hand for sensitive species or precise breeding setups.
P
- Paludarium
- A tank that combines an aquatic section with a land (terrestrial) section, home to both aquatic and land-dwelling species. See Terrariums & Terrestrial Plants.
- PAR
- "Photosynthetically Active Radiation" — the measure of light intensity that actually drives plant growth, used to match aquarium lighting to plant needs. See Aquascape Lighting Guide.
- pH
- A measure of how acidic or alkaline water is, on a scale of 0–14 with 7 neutral — different species and habitats have very different natural ranges. See Water Quality.
- Photoperiod
- The number of hours a tank's lights are on each day — usually 6–10 hours for a planted tank, balanced to encourage plants without feeding algae.
- Plakat
- A betta variety with short, rounded fins closer to the wild type, as opposed to the long-finned "halfmoon" and veiltail forms. See Betta Fish Care.
Q
- Quarantine tank (QT)
- A separate, simple tank used to hold new fish or plants for a few weeks before adding them to a main display — the single best habit for keeping disease out of an established tank.
R
- Riparium
- A tank planted mainly at and above the waterline, mimicking a riverbank, with fish kept in open water below — a less common cousin of the paludarium.
- RO/DI water
- Reverse-osmosis water further treated by deionisation — the purest practical water available to hobbyists, common in reef and precision-breeding setups.
S
- Shrimp — Neocaridina / Caridina
- The two main dwarf shrimp genera in the hobby. Neocaridina (like cherry shrimp) are hardier and more forgiving; Caridina (like Crystal Red and Taiwan Bee shrimp) need more stable, specific water. See Freshwater Shrimp Keeping.
- Stocking level
- How many/how much livestock a tank holds relative to its size and filtration capacity — overstocking is one of the most common beginner mistakes. Try our Aquarium Health Score tool.
- Substrate
- The material lining the bottom of the tank — sand, gravel, or nutrient-rich "aqua soil" for planted setups. See Aquascaping Substrates Compared.
- Sump
- A secondary tank, usually below the display tank, that houses filtration, heaters and equipment out of sight — common in larger and reef setups.
T
- Tang / Tanganyika
- Hobby shorthand for Lake Tanganyika and its cichlids — hard, alkaline water and a very different cast of species from Lake Malawi. See Lake Tanganyika Aquariums.
- Tannins
- Compounds released by driftwood and dried leaves that tint water amber or tea-brown — the signature look of blackwater tanks, and often softens/acidifies water slightly too.
- TDS
- "Total Dissolved Solids" — a single-number readout (in ppm) of everything dissolved in water, often used as a quick check alongside GH/KH for shrimp keepers especially.
U
- UV steriliser
- An inline device that uses ultraviolet light to kill free-floating algae and pathogens as water passes through it — commonly used to clear green water or reduce disease spread.
V
- Vivarium
- A fully terrestrial enclosure for land-dwelling animals and plants — the umbrella term that bioactive and paludarium setups both sit under. See Tropical Bioactive Vivarium.
W
- Water change (WC)
- Removing a portion of tank water and replacing it with fresh, treated water — the single most important recurring maintenance task in the hobby, whatever else changes.
- Wabi-Kusa
- A ball or mound of emersed-grown aquatic plants bound together, often displayed partly out of water — a decorative technique that bridges aquascaping and terrarium keeping.
Z
- Zeolite
- A porous mineral media that adsorbs ammonia directly from water — sometimes used as emergency chemical filtration, though it isn't a substitute for a properly cycled tank.