A free, self-paced textbook in 8 chapters. Read a chapter, then drill it with the 204 companion flashcards using spaced repetition.
An aquarium is an enclosed tank that holds water, aquatic life, and often plants. The hobby of maintaining these systems is called fishkeeping, and it spans everything from small d...
The single most important concept in fishkeeping is the nitrogen cycle, the biological process that converts fish waste into less harmful compounds. Fish excrete ammonia through th...
Beyond the nitrogen cycle, several other water parameters shape fish health. pH measures acidity on a scale where 7 is neutral, lower values are acidic, and higher values are basic...
Filtration is the mechanical and biological heart of the aquarium. It removes debris, supports the bacteria of the nitrogen cycle, and may include chemical media to polish the wate...
Live aquatic plants do far more than decorate. They consume nitrates, produce oxygen, compete with algae for nutrients, and offer hiding places for shy or juvenile fish. Beginner-f...
Choosing fish wisely begins with research and a healthy skepticism toward the old rule of one inch of fish per gallon. That guideline ignores differences in bioload, the amount of...
Some fishkeeping paths branch off into more specialized territory. Reef tanks represent the demanding end of the saltwater hobby, building a living coral ecosystem rather than just...
Beyond equipment and biology, fishkeeping is shaped by a particular mindset. Patience is the throughline: aquariums reward slow, steady additions and careful observation rather tha...