The Nitrogen Cycle Explained
The most important concept in fishkeeping is the Nitrogen Cycle. When fish produce waste, or when uneaten food decays, it releases ammonia into the water. Ammonia is highly toxic to aquatic life, burning their gills and causing severe distress. In a mature aquarium, colonies of beneficial bacteria naturally form in the filter media and substrate. The first type of bacteria consumes ammonia and converts it into nitrite (which is also highly toxic). A second type of bacteria then develops to consume the nitrite, converting it into nitrate. Nitrate is much less toxic and is removed through regular partial water changes.
Cycling a New Tank
A new aquarium has no beneficial bacteria. This is why adding fish on the first day usually results in disaster. The tank must be "cycled" before livestock is added. This involves introducing an ammonia source (such as pure liquid ammonia or fish food) to an empty tank and running the filter continuously. Using a liquid test kit, you monitor the levels of ammonia, nitrite, and nitrate over several weeks. The cycle is complete only when the tank can process a dose of ammonia completely into nitrate within 24 hours, leaving zero ammonia and zero nitrite.
Vital Water Parameters
- Ammonia & Nitrite: Must always read 0 parts per million (ppm) in a cycled tank with fish.
- Nitrate: Should generally be kept low (often below 20-40 ppm depending on species) through weekly water changes. Live plants also help absorb nitrates.
- pH: Measures acidity or alkalinity. Rather than chasing a specific pH number with chemicals, stability is paramount. Most captive-bred fish can adapt to a stable pH, but sudden fluctuations are dangerous.
- Temperature: Tropical fish require a stable temperature maintained by a reliable heater. Even small, rapid changes in temperature can weaken immune systems.
Dechlorination
Municipal tap water is treated with chlorine or chloramine to make it safe for human consumption. However, these chemicals will instantly kill the beneficial bacteria in your filter and burn the gills of your fish. Every drop of new water added to an aquarium must be treated with a water conditioner (dechlorinator) before it comes into contact with the tank environment.