Aquarium Glossary: 100 Terms Every Fishkeeper Should Know
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emilynakatani
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17 min read
Table of Contents
Introduction
The aquarium hobby comes with its own vocabulary, and understanding these aquarium glossary terms is essential for every fishkeeper—whether you are a complete beginner setting up your first tank in Singapore or a seasoned hobbyist looking to brush up on terminology. From water chemistry to aquascaping techniques, this comprehensive A-to-Z glossary covers 100 terms you will encounter regularly in the hobby.
At Gensou, with over 20 years of experience in the aquascaping industry from our studio at 5 Everton Park, we have compiled this reference guide to help Singapore’s fishkeeping community communicate more effectively and understand the science behind their aquariums.
A–C
| Term | Definition |
|---|---|
| Acclimation | The process of gradually adjusting a fish to new water conditions (temperature, pH, hardness) to reduce shock. Typically done by floating the transport bag and slowly mixing tank water in over 30–60 minutes. |
| Activated Carbon | A chemical filtration media that adsorbs dissolved organic compounds, medications, and odours from aquarium water. Must be removed when medicating fish. |
| Aerobic Bacteria | Beneficial bacteria that require oxygen to convert ammonia to nitrite and nitrite to nitrate in the nitrogen cycle. |
| Algae | Simple photosynthetic organisms that grow in aquariums. Some types are harmless or even beneficial; others (like blue-green algae) can be problematic. |
| Ammonia (NH3/NH4+) | A toxic compound produced by fish waste, decaying food, and decomposing organic matter. Must be maintained at 0 ppm in established tanks. |
| Anaerobic | An oxygen-free environment. Anaerobic bacteria in deep substrate can convert nitrate to nitrogen gas, but anaerobic pockets can also produce toxic hydrogen sulphide. |
| Aqua Soil | A nutrient-rich substrate designed for planted aquariums. Lowers pH and provides essential nutrients for plant root growth. Popular brands include ADA Amazonia and Tropica. |
| Aquascape | The art of arranging aquatic plants, rocks, driftwood, and other elements in an aquarium to create a visually appealing underwater landscape. |
| Beneficial Bacteria | Nitrifying bacteria (primarily Nitrosomonas and Nitrobacter) that colonise filter media and surfaces, processing toxic ammonia and nitrite into less harmful nitrate. |
| Biofilm | A thin layer of microorganisms (bacteria, algae, fungi) that forms on submerged surfaces. An important food source for shrimp and fry. |
| Bioload | The total amount of biological waste produced by the living organisms in an aquarium. Higher bioloads require more filtration and more frequent water changes. |
| Blackwater | Water stained brown by tannins released from driftwood, Indian almond leaves, or peat. Lowers pH and mimics the natural habitat of many Southeast Asian fish species. |
| Brackish | Water that is a mix of fresh and saltwater, with a specific gravity between 1.005 and 1.015. Home to species like mudskippers and archerfish. |
| Breeding Trap | A small container placed inside the tank to isolate pregnant livebearers or protect fry from being eaten by adults. |
| Buffer | A chemical or substance that stabilises pH, preventing rapid fluctuations. Crushed coral and commercial buffers are commonly used. |
| Canister Filter | An external pressurised filter that sits below the tank. Provides excellent mechanical, biological, and chemical filtration for medium to large aquariums. |
| Carpeting Plant | A low-growing aquatic plant that spreads across the substrate to create a lawn-like carpet effect. Popular species include Monte Carlo, Dwarf Hairgrass, and HC Cuba. |
| Chloramine | A disinfectant used in tap water (including Singapore’s PUB water supply) that is toxic to fish. Removed with water conditioners like Seachem Prime. |
| CO2 Injection | The practice of adding carbon dioxide to a planted aquarium to promote faster, healthier plant growth. Can be done via pressurised systems or DIY yeast-based methods. |
| Community Tank | An aquarium housing multiple species of fish that coexist peacefully. Requires careful species selection to avoid aggression and compatibility issues. |
| Cycling | The process of establishing beneficial bacteria colonies in a new aquarium before adding fish. Typically takes 2–6 weeks (often faster in Singapore’s warm climate). |
D–F
| Term | Definition |
|---|---|
| Dechlorinator | A water conditioner that neutralises chlorine and chloramine in tap water, making it safe for aquarium use. |
| Detritus | Organic waste matter that accumulates in the tank, including fish waste, uneaten food, and decaying plant matter. |
| Diatoms | Brown algae commonly seen in new aquariums. Usually harmless and temporary, disappearing as the tank matures. |
| Dissolved Oxygen (DO) | The amount of oxygen present in the water, essential for fish respiration. Increased by surface agitation and aeration; decreased by high temperatures. |
| Dosing | The practice of adding liquid fertilisers, trace elements, or CO2 to an aquarium on a regular schedule to support plant growth. |
| Dragon Stone | A porous, textured rock popular in aquascaping for its dramatic, craggy appearance. Inert (does not affect water chemistry). |
| Driftwood | Natural wood used as hardscape in aquariums. Releases tannins that lower pH and create blackwater conditions. Malaysian driftwood and Manzanita are popular choices. |
| Dropsy | A condition characterised by a bloated abdomen and raised “pinecone” scales, caused by fluid retention due to organ failure or bacterial infection. Difficult to treat. |
| Dry Start Method (DSM) | A technique for establishing carpeting plants by growing them emersed (above water) in a humid, sealed tank before flooding. Reduces algae risk during the initial growth phase. |
| Emersed | Growing above the waterline. Many aquatic plants can grow both emersed and submersed, often looking quite different in each form. |
| Epiphyte | A plant that grows attached to surfaces (rocks, wood) rather than rooted in substrate. Anubias, Java Fern, and Bucephalandra are common aquarium epiphytes. |
| Fertiliser (Liquid) | Nutrient solutions added to the water column to feed aquatic plants. Includes macronutrients (NPK) and micronutrients (iron, manganese, etc.). |
| Filter Media | Materials placed inside a filter to perform mechanical (sponge, floss), biological (ceramic rings, bio balls), or chemical (activated carbon, Purigen) filtration. |
| Fishless Cycling | Cycling a new tank by adding an ammonia source (pure ammonia or decomposing food) without any fish present. The most humane method of establishing beneficial bacteria. |
| Flaring | A display of aggression or territorial behaviour in bettas, where the fish extends its gill covers and fins to appear larger. |
| Flow Rate | The volume of water a filter or pump moves per hour, typically measured in litres per hour (LPH). Should be matched to tank size and the species kept. |
| Fry | Newly hatched or very young fish. Fry are typically tiny and require specialised food such as infusoria, baby brine shrimp, or powdered fry food. |
G–I
| Term | Definition |
|---|---|
| GH (General Hardness) | A measure of dissolved calcium and magnesium in the water. Affects the health of fish, shrimp, and plants. Measured in degrees (dGH) or ppm. |
| Gravel Vacuum | A siphon tool used during water changes to remove detritus from the substrate while draining water. |
| Green Water | Water that has turned green due to a bloom of free-floating single-celled algae. Often caused by excess light and nutrients. Can be cleared with UV sterilisers or blackouts. |
| Hang-on-Back Filter (HOB) | A filter that hangs on the rear wall of the aquarium, drawing water up through a siphon tube and returning it via a spillway. Popular for small to medium tanks. |
| Hardscape | The non-living structural elements in an aquascape, including rocks, driftwood, and stones. Forms the foundation of the design. |
| Heater | A device that warms aquarium water to a set temperature. Less critical in Singapore’s tropical climate but useful for maintaining precise temperatures. |
| Hospital Tank | See Quarantine Tank. A separate, simply equipped tank used to isolate and treat sick or injured fish. |
| Ich (Ichthyophthirius multifiliis) | A common parasitic disease causing white salt-grain-sized spots on the body and fins. Highly contagious but treatable with raised temperatures and medication. |
| Indian Almond Leaf (Ketapang) | Dried leaves of the Terminalia catappa tree, used to release tannins into aquarium water. Lowers pH, has mild antibacterial properties, and is popular with betta and shrimp keepers in Southeast Asia. |
| Inline Diffuser | A CO2 diffusion device installed within the filter’s return tubing, dissolving CO2 directly into the water flow for maximum efficiency. |
| Invertebrate | An animal without a backbone. In the aquarium hobby, this typically refers to shrimp, snails, and crabs. |
| Iwagumi | A Japanese aquascaping style using carefully arranged stones as the primary focal point, with minimal planting (usually a single carpeting species). Named after the traditional rock garden arrangement. |
J–L
| Term | Definition |
|---|---|
| Java Fern | (Microsorum pteropus) A hardy, low-maintenance epiphytic plant that thrives attached to rocks or driftwood. One of the best beginner plants. |
| Java Moss | (Taxiphyllum barbieri) A versatile, easy-to-grow moss used for carpet effects, breeding sites, and decorating hardscape. Thrives in a wide range of conditions. |
| KH (Carbonate Hardness) | A measure of the water’s buffering capacity—its ability to resist changes in pH. Higher KH means more stable pH. Measured in dKH or ppm. |
| Laterite | An iron-rich clay substrate used beneath gravel in planted tanks to provide nutrients to plant roots. |
| LED Lighting | Light-emitting diode technology, now the standard for aquarium lighting. Energy-efficient, long-lasting, and available in spectrums suitable for plant growth. |
| LFS (Local Fish Shop) | A common abbreviation in the fishkeeping community referring to a local aquarium retail store. |
| Lily Pipe | Glassware (inlet and outlet pipes) used with canister filters in aquascaping for a clean, minimalist aesthetic. Made of clear glass or acrylic. |
| Livebearer | A fish that gives birth to free-swimming young rather than laying eggs. Guppies, mollies, platies, and swordtails are common livebearers. |
| Live Rock | Porous rock colonised by beneficial bacteria and organisms, used primarily in marine aquariums for biological filtration. |
| Low Tech | A planted tank approach that does not use CO2 injection, relying instead on low-light plants and moderate lighting. Lower maintenance and cost compared to high-tech setups. |
M–O
| Term | Definition |
|---|---|
| Macronutrients | The primary nutrients required by aquatic plants in larger quantities: nitrogen (N), phosphorus (P), and potassium (K). |
| Matured Tank | An aquarium that has been running long enough for the nitrogen cycle to be fully established and the ecosystem to stabilise. Typically after 3–6 months. |
| Mechanical Filtration | The physical removal of suspended particles and debris from the water using sponges, filter floss, or pads. |
| Micronutrients | Trace elements required by plants in small quantities, including iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and boron (B). |
| Mini Cycle | A temporary disruption to the nitrogen cycle, often caused by cleaning filter media too aggressively, medicating, or adding many new fish at once. Results in brief ammonia or nitrite spikes. |
| Molting | The process by which shrimp and other crustaceans shed their exoskeleton to grow. Moulting shrimp are vulnerable and need hiding places. |
| Nano Tank | A small aquarium, typically under 40 litres. Popular in Singapore for desktop and small-space setups, especially for bettas and shrimp. |
| Nature Aquarium | An aquascaping philosophy pioneered by Takashi Amano that recreates natural landscapes underwater using plants, rocks, and driftwood in harmonious compositions. |
| Nitrate (NO3-) | The end product of the nitrogen cycle. Less toxic than ammonia or nitrite, but should be kept below 20–40 ppm through regular water changes. A nutrient source for plants. |
| Nitrite (NO2-) | An intermediate product in the nitrogen cycle, produced when beneficial bacteria convert ammonia. Toxic to fish; must be maintained at 0 ppm. |
| Nitrogen Cycle | The biological process by which ammonia is converted to nitrite and then to nitrate by beneficial bacteria. The foundation of all successful aquarium keeping. |
| Old Tank Syndrome | A gradual decline in water quality in a neglected tank, where pH drops and nitrate accumulates over time. Fish may acclimate slowly but new additions often die. |
| Osmotic Stress | Physiological stress caused by sudden changes in water salinity or mineral content, affecting a fish’s ability to regulate water and salts in its body. |
| Overstocking | Keeping more fish than the aquarium and its filtration can safely support, leading to poor water quality, stress, aggression, and disease. |
P–R
| Term | Definition |
|---|---|
| PAR (Photosynthetically Active Radiation) | A measure of the light available for photosynthesis, used to evaluate aquarium lighting for planted tanks. Measured in micromoles per square metre per second. |
| Paludarium | A setup that combines aquatic and terrestrial elements, featuring both underwater and above-water plants and animals. |
| Parameters | The measurable water quality values in an aquarium, including pH, ammonia, nitrite, nitrate, GH, KH, and temperature. |
| Pearl (Pearling) | The visible release of oxygen bubbles from the leaves of aquatic plants during active photosynthesis. A sign of healthy, well-lit, CO2-supplemented plant growth. |
| pH | A scale (0–14) measuring how acidic or alkaline water is. 7.0 is neutral. Most tropical freshwater fish thrive between 6.5 and 7.5. Singapore tap water is typically around 7.0–7.5. |
| Photoperiod | The duration of time aquarium lights are on each day. Typically 6–10 hours for planted tanks; longer periods encourage algae growth. |
| Plakat | A short-finned betta variety, closer in appearance to wild bettas. Faster and hardier than long-finned varieties. |
| Planted Tank | An aquarium that features live aquatic plants as a primary element, often requiring specialised lighting, substrate, and fertilisation. |
| Powerhead | A submersible pump used to create water circulation within the tank. Helps distribute heat, CO2, and nutrients evenly. |
| Protein Skimmer | A filtration device used primarily in marine aquariums that removes dissolved organic compounds by creating a column of fine bubbles. |
| Quarantine Tank | A separate, simply equipped tank used to isolate new fish before introduction to the main tank, or to treat sick fish away from the community. |
| Refugium | A secondary chamber or tank connected to the main aquarium, used to grow beneficial organisms like macroalgae or copepods, primarily in marine setups. |
| Reverse Osmosis (RO) | A water purification process that removes minerals, chemicals, and impurities. RO water is used to create custom water parameters, especially for sensitive species like Caridina shrimp. |
| Root Tab | A solid fertiliser capsule pushed into the substrate near plant roots, providing nutrients directly to root-feeding plants like Cryptocorynes and Amazon Swords. |
S–U
| Term | Definition |
|---|---|
| Schooling Fish | Fish species that naturally swim together in coordinated groups. Tetras, rasboras, and corydoras are popular schooling fish that should be kept in groups of six or more. |
| Seiryu Stone | A grey-blue limestone popular in aquascaping, especially Iwagumi layouts. Raises KH and pH slightly over time. |
| Shrimp | Freshwater invertebrates popular in planted tanks. Neocaridina (cherry shrimp) are hardy beginners’ choices; Caridina (crystal shrimp) require more precise water parameters. |
| Siphon | A tube used to drain water from the tank by gravity, typically during water changes and substrate cleaning. |
| Slime Coat | A mucus layer covering a fish’s body that acts as a barrier against bacteria, parasites, and physical damage. Stress can thin the slime coat, increasing vulnerability. |
| Snail | Freshwater gastropods commonly found in aquariums. Nerite snails are valued algae eaters; pest snails (bladder, ramshorn) can multiply rapidly. |
| Specific Gravity | A measure of water density compared to pure water, used primarily in marine and brackish aquariums to determine salinity. |
| Sponge Filter | A simple, air-driven filter that uses a sponge as both mechanical and biological filtration. Ideal for fry tanks, quarantine tanks, and shrimp tanks. |
| Stocking Level | The number and size of fish relative to the aquarium’s capacity. Overstocking leads to poor water quality and stress. |
| Submersed | Growing underwater. Plants grown submersed often look different from their emersed (above-water) forms. |
| Substrate | The material covering the bottom of the tank. Options include gravel, sand, aqua soil, and clay-based substrates, each with different properties. |
| Surface Agitation | Movement at the water’s surface that promotes gas exchange, increasing dissolved oxygen and releasing CO2. Created by filter outlets, air stones, or powerheads. |
| Swim Bladder | An internal gas-filled organ that allows fish to control their buoyancy. Swim bladder disorder causes difficulty maintaining normal position in the water. |
| Tannins | Organic compounds released by driftwood, leaves, and seed pods that stain water amber-brown, lower pH, and have mild antibacterial properties. |
| TDS (Total Dissolved Solids) | A measure of all dissolved substances in water, including minerals, salts, and organic matter. Measured in ppm using a TDS meter. Critical for shrimp keeping. |
| Trimming | The regular cutting and pruning of aquatic plants to maintain the desired shape and density in a planted aquarium. |
| UV Steriliser | A device that passes aquarium water past an ultraviolet light, killing free-floating algae, bacteria, and parasites. Effective against green water and some diseases. |
| Undergravel Filter | An older filtration system that draws water down through the substrate. Largely replaced by more efficient modern filtration methods. |
V–Z
| Term | Definition |
|---|---|
| Velvet (Oodinium) | A parasitic disease causing a fine gold or rust-coloured dusting on the fish’s body. Often mistaken for ich but finer in texture. Treated with copper-based medications. |
| Wabi-Kusa | A Japanese style of displaying aquatic and semi-aquatic plants grown on a ball of substrate, placed in a small open container of water. |
| Water Change | The routine practice of removing a portion of tank water and replacing it with fresh, dechlorinated water. Essential for diluting nitrates and replenishing minerals. |
| Water Column | The body of water in the tank, as distinct from the substrate. Plants that feed from the water column absorb nutrients through their leaves. |
| Water Conditioner | A liquid treatment that neutralises chlorine, chloramine, and heavy metals in tap water. Essential for making tap water safe for aquarium use. |
| Wavemaker | A pump that creates alternating water currents, simulating natural wave action. Primarily used in marine tanks but sometimes in large freshwater setups. |
| Wet/Dry Filter | A filtration system where water trickles over filter media exposed to air, maximising oxygen contact for superior biological filtration. |
| Zoning | The practice of dividing an aquascape into distinct areas (foreground, midground, background) with different plant heights and types to create depth and visual interest. |
Singapore-Specific Terms
The local fishkeeping scene in Singapore has its own commonly used terms and references:
| Term | Definition |
|---|---|
| LFS | Local Fish Shop—any brick-and-mortar aquarium retail store in Singapore |
| Ketapang | The Malay name for Indian almond leaves, widely used in Singapore’s fishkeeping community |
| PUB Water | Tap water supplied by Singapore’s Public Utilities Board; treated with chloramine and generally soft with a pH of 7.0–7.5 |
| Chiller | A cooling device sometimes necessary in Singapore when aquarium temperatures exceed safe levels, especially for marine tanks and sensitive shrimp species |
| AQ | Short for AquaticQuotient.com, Singapore’s longest-running aquarium hobbyist forum |
| NEA Fogging | Insecticide fogging conducted by the National Environment Agency for dengue prevention; aquarists must protect tanks by covering them and disabling air pumps during fogging sessions |
Frequently Asked Questions
What are the most important terms a beginner should learn first?
Focus on understanding the nitrogen cycle and its key terms (ammonia, nitrite, nitrate, cycling, beneficial bacteria), basic equipment terms (filter, substrate, water conditioner), and water parameter terms (pH, GH, KH). These form the foundation of all fishkeeping knowledge and will help you maintain a healthy aquarium from day one.
What does “high tech” vs “low tech” mean for planted tanks?
A high-tech planted tank uses CO2 injection, strong lighting, and regular fertiliser dosing to support demanding plant species and fast growth. A low-tech tank relies on ambient CO2, moderate or low lighting, and hardy plant species that require less supplementation. Low-tech is more beginner-friendly and lower maintenance, while high-tech produces more dramatic, lush results.
Why do fishkeepers in Singapore talk about “ketapang” so much?
Ketapang (Indian almond) trees grow abundantly throughout Southeast Asia, making the dried leaves easily accessible in Singapore. They are a natural, inexpensive way to condition water for bettas, shrimp, and other species that prefer slightly acidic, tannin-rich conditions. Many local hobbyists collect them from parks and nature areas or buy them cheaply from local fish shops.
Are there any aquarium terms that mean different things in different countries?
Yes. For example, “gallon” differs between the US (3.78 litres) and the UK (4.55 litres), which can cause confusion when reading international advice on stocking levels or dosing. In Singapore, we use litres as the standard measurement. Additionally, fish common names vary by region—what Singaporeans call a “flower horn” may be listed under different names elsewhere. Always verify using scientific (Latin) names when possible.
Build Your Knowledge With Gensou
Understanding aquarium terminology is the first step towards becoming a confident, capable fishkeeper. Whether you are just learning the basics or diving into advanced aquascaping concepts, knowledge is the foundation of every successful aquarium.
At Gensou, we have spent over 20 years sharing our passion for aquascaping with Singapore’s hobbyist community from our studio at 5 Everton Park. Our team is always happy to explain concepts, answer questions, and help you put knowledge into practice.
Want to learn more? Get in touch with our team for personalised advice, browse our online shop for quality equipment and supplies, or explore our custom aquarium services to see these concepts brought to life in a professionally designed aquascape.
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