Corydoras catfish are social shoalers that require companions of their own species. Absolute minimum: 6 of the same species (not "6 mixed cories"). Mixed-species groups don't shoal - each species needs its own 6+. Ideal numbers: 8-10+ for active foraging behavior, courtship displays, and breeding. Tank requirements: minimum 20-gallon long for the smaller species (pygmaeus, habrosus, hastatus). 29-gallon+ for medium species (panda, sterbai, julii, trilineatus). 40-gallon breeder for the bronze + emerald cories (paleatus, aeneus). Substrate: sand or smooth fine gravel ONLY. Sharp gravel destroys their barbels (sensory whiskers). Once damaged, barbels rarely regrow. Tankmates: peaceful community fish - tetras, rasboras, dwarf gouramis, livebearers. AVOID with: angelfish (eat juvenile cories), oscars + larger cichlids, aggressive plecos. Diet: not just bottom-feeders eating leftovers. Need dedicated sinking pellets (Hikari Sinking Wafers, Repashy Bottom Scratcher) + occasional bloodworms or live blackworms. Group dynamics: solo cory = stressed, hiding, dim color. Add 5-6 more and watch the entire personality change overnight.
The full Q&A library answers the most-searched aquarium questions. Browse calculators, glossary, and disease database for related help.
Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.
How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.
What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.
How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.
Saltwater livestock · Freshwater livestock · Coral catalog · Care library · Q&A library (222) · Glossary (127) · Disease database (50) · Calculators (29) · Interactive tools (7) · Husbandry deep-dives · DIY projects · State legality directory