Fish

Fishkeeping is really water-keeping: the aquarium hobby's one great secret is the nitrogen cycle, in which beneficial bacteria convert toxic ammonia from fish waste into nitrite and then into relatively harmless nitrate. 'Cycling' a tank — growing that bacterial colony for 4–6 weeks before the fish arrive — prevents the new-tank losses that end most beginners' careers, and a weekly partial water change plus a liquid test kit prevents nearly everything else. Stock by temperament and water chemistry, not by looks alone: schooling species need groups of six or more, territorial cichlids need architecture and space, and a fish sold at 3 cm may be a 30 cm tankbuster (the common pleco says hello). Our catalog is organized by the hobby's classic groups — livebearers, tetras, cichlids, labyrinth fish, catfish, coldwater, barbs and the wonderful oddballs — each with its own care profile.