Whether your aquarium plants need CO2 depends on light intensity + plant species. No-CO2 tanks (low light): anubias, java fern, java moss, cryptocoryne, amazon sword, vallisneria, hornwort, water sprite, dwarf sagittaria. Run light at 4,000-6,500K, 6-7 hours, no fertilizer or 1x weekly Flourish Comprehensive. Liquid carbon tanks (medium light): rotala rotundifolia, ludwigia repens, cabomba, bacopa, alternanthera. Dose Seachem Excel or Tropica Premium. Caveat: Excel kills vallisneria and damages anacharis. Pressurized CO2 tanks (high light, high tech): required for HC cuba, dwarf hairgrass carpets, monte carlo, glossostigma, riccia, blyxa, most stem plant carpets, AR mini, all reds. Target 25-30 ppm CO2 (use a drop checker + KH/pH math). Inject during photoperiod only. Cost: liquid carbon $15/month, full pressurized CO2 setup $250-450 one-time + $20/refill every 4-6 months. Plant nutrition stack: light + CO2 + macros (NPK) + micros (trace) + substrate. Skip any one and the others can't compensate.
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.
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