An aquarium is a beautiful addition to a home. But fish suddenly dying is the #1 reason beginners give up. The fix: start with the basics done right.

Tank size: bigger is easier

Counterintuitive: small tanks are harder than large ones. Larger tanks dilute waste, have thermal stability, support more fish.

Recommended starter: 20+ gallons. Avoid 5-gallon "betta tanks" or smaller.

Required equipment

  • Tank: $30–60 for 20–29 gallons.
  • Filter: rated for tank size or larger. $25–50.
  • Heater: 5 watts per gallon. $20–30.
  • Substrate: gravel ($15–30) or sand ($10–25).
  • Dechlorinator: tap water has chlorine. Seachem Prime. $5–10.
  • Test kit: API Master Test Kit. $30.
  • Net, bucket, lighting.

Total starter: ~$150–250.

The cycling process

Before fish, "cycle" the tank. This builds beneficial bacteria converting toxic ammonia to nitrite to nitrate. Without cycling, fish die from ammonia poisoning within days.

Fishless cycling (recommended)

  1. Set up tank with water, dechlorinator, substrate, decor.
  2. Add ammonia source (pure ammonia or fish food).
  3. Wait 4–6 weeks. Test daily.
  4. Ammonia spikes then drops to zero, then nitrite spikes then drops = cycled.
  5. Add fish.

Tank stocking

"1 inch of fish per gallon" is rough. For 20 gallons: up to 20 inches of small community fish. Better: research specific species.

Recommended starter fish

Easy community:

  • Neon tetras: peaceful, schooling.
  • Cardinal tetras.
  • Cherry barbs.
  • Harlequin rasboras.
  • Platies.
  • Mollies.
  • Corydoras catfish.

Avoid for beginners: Discus, African cichlids, goldfish in small tanks, bettas with flowing-finned tankmates.

Adding fish: do it slowly

Don't add all fish at once even after cycling. First batch: 4–5 fish. Wait 2 weeks. Test water. Add next batch. Total stocking: 4–8 weeks.

Acclimating new fish

Float method: float bag in tank 15–20 min, open bag and add cup of tank water, wait 15 min, repeat. After 30 min, net fish out and add to tank. Discard bag water.

Daily care

  • Feed once or twice daily, only what fish eat in 1–2 minutes.
  • Watch for unusual behavior.
  • Check temperature.

Weekly maintenance

  • Water test: ammonia, nitrite, nitrate, pH.
  • 20–25% water change with siphon.
  • Vacuum substrate during change.
  • Glass cleaning.

Monthly maintenance

  • Rinse filter media in OLD tank water (NOT tap water).
  • Check heater and filter.
  • Trim plants.

Common beginner mistakes

  1. Skipping the cycle.
  2. Overstocking.
  3. Overfeeding.
  4. Tap water without dechlorinator.
  5. Not testing water.
  6. Wrong fish for tank size.
  7. Mixing aggressive and peaceful species.

Calculate tank volume

Our fish tank volume calculator takes dimensions and returns gallons. Use to plan stocking.