Guides
Concise articles you can finish in one sitting. Pair them with the fish, plant, and equipment databases when you plan a build.
Getting started
Ecosystem cycles
Ecosystem cycles: how an aquarium actually works
An overview of the five interlocking loops — nitrogen, oxygen, CO₂, water, and the new-tank break-in — with interactive SVGs and links to each in-depth article.
Read guide →The nitrogen cycle
Two-step bacterial oxidation — ammonia → nitrite → nitrate — is the most important biochemical chain in any freshwater tank. This article reviews the actual microbial ecology and how to read test-kit numbers against it.
Read guide →The oxygen cycle
Dissolved oxygen enters the tank through the surface and through photosynthesis; it leaves through fish, bacterial, and plant respiration. Understanding both sides solves more morning-gasping problems than buying an air pump.
Read guide →The CO₂ cycle
In most planted tanks above moderate light, CO₂ is the variable that sets the growth ceiling. This article explains how CO₂ dissolves, how it interacts with KH to shape pH, and how to inject it safely.
Read guide →The water cycle
Tank water is never static. It moves through evaporation, top-off, water changes, and filtration in parallel. The hidden consequences — hardness drift, mineral accumulation, gas exchange — are the most common cause of unexplained long-term failures.
Read guide →New-tank cycling: a 3–5 week protocol
What you wait for is not 'water clearing' but the colonization of your filter by nitrifying bacteria. Microbial growth curves from the literature explain what to test each week and what numbers mean the system is stable.
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