A 5-gallon tank is the smallest defensible heated, filtered freshwater setup - and stocking is limited. Best options: 1) one male betta + a couple of nerite snails. Add live plants, soft sponge filter, 25W heater. 2) cherry shrimp colony - start with 10-15 shrimp + 3-5 nerite snails. They reproduce; expect 50-100 in 6 months. 3) chili rasbora micro-school - 8-10 fish maximum. Nano peaceful fish handle the small footprint. 4) Endler's livebearer trio (1 male + 2 females, separate juveniles to avoid overstocking). What does NOT fit: goldfish (need 30+ gallons; common goldfish 75+), neon tetras (need 6+ in 10g+), guppies (need 10g+ for single trio), platies/swordtails, all gouramis except scarlet badis, all plecos, all corydoras, all African cichlids. Aquascape considerations: short footprint = limited substrate depth. Use small driftwood + small leaf litter for bettas. Foreground carpets need 2-3" substrate at minimum. Do NOT skip the heater: 5 gallons swings 5-8°F in a single day with room-temp heating cycles. 25W mini Hydor or Eheim Jager. Do NOT skip the filter: sponge filter on USB pump or a small HOB rated for 10g (oversized = better). Cycle for 3-4 weeks before adding livestock - small tanks crash fastest under uncycled conditions.
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.
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