This glossary is an extensive (and constantly updated) list of common terms in the Aquarium Hobby. Please let us know if you think something is missing.

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Acclimation/Drip Acclimation: The process of acclimatising your fish to a new environment slowly, which helps prevent stress and parameter shock. We recommend drip-acclimating for several hours before introducing fish to a new environment. (See Acclimation and Quarantine for more details)

Ammonia: (NH₃.)An inorganic compound formed in the Aquarium when organic matter (excess food, fish waste, decaying plants etc)breaks down in the water column. Extremely toxic. See #water-chemistry for more details

Ammonium: (NH₄) Similar to Ammonia, but present in extremely low pH.

Beneficial Bacteria: Bacteria cultivated within the aquarium that has beneficial effects. Often refers to the bacteria that creates the Nitrogen Cycle, as well as other bacteria that support aquatic ecosystems.

Biofilm/Aufwuchs: microscopic bacteria, fungi and other organisms that grow in aged aquariums. Essential for grazing fish and fry/babies. Includes algae and that foul smelling white fungus that grows on new driftwood. Extremely beneficial.

Bio-media/Bio-filtration: filtration media that is specifically designed to house beneficial bacteria and expose it to waterflow safely. Sintered glass, ceramic rings and plastic bio-balls are some examples of Bio-media (See Setting up your Aquarium for more details)

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‍Blackwater: water stained dark brown (like tea), usually from driftwood or leaf litter. Consists of beneficial tannins, as well as humic and fulvic acids. Extremely beneficial for most fish, but can be unpleasant to look at.

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Chloramines: Much harsher than Chlorine. Harder to remove from the water.

‍Chlorine: A harsh chemical used in drinking water to sterilise bacteria. Toxic to fish. Easily neutralised with Chlorine Neutralisers

CO2/CO2 Injection: a gas used by plants during photosynthesis. Injection into an aquarium with a diffuser
helps plants grow faster, and often improves colouration.

GH: General Hardness. Measures the general mineral (specifically Calcium and Magnesium) hardness levels in the water column. Calcium and Magnesium are essential for fish to develop healthy bone structure, form a healthy immune system and digest foods. Appropriate GH values may vary per species, so monitoring your GH levels is important. GH can easily be monitored by using a standard GH drop check test kit.

Hardscape: the non-living ornamentation in your aquarium. Usually refers to driftwood or rocks rather than plastic ornaments.

Ich: A common aquarium parasite (Ichthyophthirius multifiliis) that appears as small white spots, primarily on the gills and fins of your fish. Other symptoms may include loss of appetite, scratching, lethargy and death. Caused by stress and/or improper water parameters. Also known as white spot disease (See the Disease Database for more details.)

KH: Carbonate Hardness measurement. Used to measure the amount of Carbonates in the water column, which act as a pH buffer.Low KH values can cause pH swings, which can be lethal to your fish. Extremely high KH values can cause your pH to go too high, leading to alkaline water which may not be beneficial to your fish. Low KH aquariums are typically fairly acidic, which can be problematic as well. Monitoring KH is fairly important and can easily be done with a KH drop testing kit.

Mechanical filtration: Filtration systems/filtration media designed to trap and remove large particles of matter from the water column. Sponges and filter floss are the most common forms of mechanical filtration.

Nitrates: (NO₃+) A chemical compound often found in the water column of Aquatic environments. The end result of the Nitrogen Cycle. Toxic in amounts above 40ppm.

Nitrites: (NO₂-) Less toxic than NH₃/NH₄, but still poisonous to your fish. A natural byproduct of the Nitrogen Cycle, and rapidly used up during that process. Measurable amounts in your water column indicate an incomplete or crashing Nitrogen Cycle.

Nitrogen Cycle: The process in which Beneficial Bacteria in your filter converts toxic Ammonia into Nitrites (NO₂-) and then into far less dangerous Nitrates (NO₃+). This process is vital to your aquarium's health and must be present before fish are introduced.

pH: the Power of Hydrogen. A scale used to measure the acidity or alkalinity of water. An important parameter to test for as different species have vastly different requirements, and will not be happy or healthy outside their ideal pH.

Phosphates: Phosphates are a mineral that buildup in the water column when organic matter decompose (organic phosphates) or fertiliser (inorganic mineral phosphates). May cause algae blooms (see Phosphates for more details)

Readily absorbed by plants and consumed by certain anaerobic bacteria.

Reverse Osmosis (RO) Water: Water that has been purified by Reverse Osmosis. Completely pure and must be demineralised. Sometimes called RODI Water.

Substrate: the layer of gravel, sand or soil that covers the bottom of your tank. Tanks that don't have this layer are referred to as bare-bottom tanks.

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