Tap water + dechlorinator = safe for most aquarium tanks. What's in tap water: chlorine (kills bacteria), chloramine (chlorine + ammonia, harder to neutralize), heavy metals (copper, lead in some plumbing), TDS varies by region (50-500 ppm typical). Dechlorinator basics: Seachem Prime (the standard - dechlorinates + detoxifies ammonia), API Stress Coat (with aloe vera), Tetra AquaSafe. Add per dose to all replacement water. Test your tap: pH (5.5-9 found in US tap), KH (varies wildly), TDS, chlorine level. Some regions have hard water perfect for African cichlids; others are soft + ideal for discus. When tap water is NOT safe: 1) discus + apistogramma + crystal red shrimp need RO water + remineralizer. 2) reef tanks need RO/DI (zero TDS) due to phosphate, silicate, copper in tap. 3) areas with high copper plumbing kill shrimp. RO/DI alternatives: 50-100 GPD home unit ($150-300), grocery store water exchange (~$0.40/gal but contaminated risk), bottled distilled (~$1/gal for emergencies only). Don't use: softened water (sodium replaces calcium - bad for fish) or filtered drinking water (still has TDS).
The full Q&A library, calculators, diseases, glossary, and interactive tools answer the most-searched aquarium questions.
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