Goldfish compatibility guide. 5 compatible tankmates + 5 species to avoid + temperament + size + water-chemistry guidance.
Best companions are other goldfish of similar size + body type. Mix fancy + fancy, single-tail + single-tail.
Coldwater bottom dweller, peaceful, eats leftover food.
Coldwater algae eater, peaceful, prefers cool fast-flow water.
Coldwater snail; large enough not to be eaten.
Coldwater schooling fish, peaceful, fits goldfish parameters.
Goldfish need 65-72°F; tropicals need 76-82°F. Mismatch kills both.
Plecos suck slime coat off goldfish at night. Kills goldfish slowly.
Aggressive + hot-water requirement.
Tropical + delicate fins.
Goldfish eat anything that fits in their mouth.
Use the stocking calculator to verify your specific plan. Browse stocking ideas by tank size for proven setups, or read the Goldfish care guide for full husbandry details.
Browse all tankmate guides.
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.
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