Oscar Cichlid compatibility guide. 6 compatible tankmates + 5 species to avoid + temperament + size + water-chemistry guidance.
Fast schooling fish, too big for adult oscars to eat. Schools of 6+.
Tough enough to handle oscars. Similar habits.
Larger peaceful cichlid, comparable size to oscars.
Big armored algae eater. Larger plecos are oscar-proof.
Aggressive enough to coexist; needs equally large tank.
Aggressive cichlid, similar water + size requirements.
Adult oscars eat anything that fits in their mouth. They have big mouths.
Become oscar food.
Eaten immediately.
Eaten when they leave hiding.
Pairs work, but unpaired oscars kill each other. Better singles or established bonded pairs.
Use the stocking calculator to verify your specific plan. Browse stocking ideas by tank size for proven setups, or read the Oscar Cichlid 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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