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 a fish display. They require a protein skimmer to remove organic waste before it breaks down, return pumps and powerheads for strong water flow, spectrum-tuned high-output LEDs, a heater, and often controllers that monitor parameters around the clock. Corals themselves are animals rather than plants and are divided into soft corals, large polyp stony (LPS) corals, and small polyp stony (SPS) corals, each with different lighting and flow needs. PAR (photosynthetically Active Radiation) targets typically range from 100 to 300 for soft corals and 250 to 450 for SPS. Reef keepers also dose calcium, magnesium, and alkalinity to support coral skeletal growth, and many use a sump with a refugium section filled with macroalgae such as chaeto to export nutrients.
African cichlids from Lakes Tanganyika, Malawi, and Victoria are another specialty, known for vivid color and active behavior. They thrive in hard, alkaline water with pH between 7.8 and 8.5 and appreciate elaborate rockwork that provides territory and breaks lines of sight. South American cichlids occupy a different niche: angelfish, Severums, and Oscars are popular, while discus stand apart for their round, colorful bodies and demanding requirements, including warm, clean water between 82 and 86°F (28 to 30°C). Saltwater parameters for fish-only and reef tanks include a specific gravity between 1.023 and 1.025 measured with a hydrometer, a pH of 8.1 to 8.4, and temperatures around 75 to 78°F.
Coldwater fishkeeping centers on goldfish and koi. Goldfish need cool water, strong filtration, and more space than most beginners expect, with fancy varieties such as orandas and ranchus requiring 20 to 30 gallons or more and common goldfish needing far larger tanks. With proper care, goldfish can live 10 to 20 years or longer. Koi push this further into outdoor ponds of 1,000 gallons or more, where they can reach impressive sizes and live for decades. Across all these specialties, the same lesson applies: research the specific needs of the fish before acquiring them and build the system around those requirements rather than trying to retrofit an unsuitable tank.