FastAquatics

Aquarium stocking ideas by tank size

10 tank-size stocking guides. Each page lists multiple themed setups (community, reef, cichlid, planted, biotope) with exact species + counts + notes - skip the "what fish should I get" research and pick a proven plan.

5-gallon stocking ideas5g is the realistic minimum for ANY aquarium. Suitable for solo betta, shrimp colonies, or 1-2 micro fish. Below 5g is unfair to most species.4 themed setups10-gallon stocking ideas10g is the most-flexible nano size. Supports community freshwater, planted nano, shrimp + dwarf fish, single betta with tankmates.4 themed setups20-gallon stocking ideas20g (long preferred) opens up community + nano-reef + breeding setups. The 30-inch footprint of a 20g long is the sweet spot.4 themed setups29-gallon stocking ideas29g is the sweet-spot community size. Standard 30"x12"x18" footprint allows schools + bottom dwellers + a centerpiece pair without crowding.4 themed setups40-gallon stocking ideas40g breeder (36"x18") is widely considered the best mid-range tank. Wider footprint = better aquascape + nano reef + breeding.4 themed setups55-gallon stocking ideas55g (48"x13"x21") is narrow but long. Best for community freshwater + smaller mbuna + larger schools. NOT ideal for reef due to narrow depth.4 themed setups75-gallon stocking ideas75g (48"x18") is the sweet spot for serious reef + larger freshwater. The 18-inch depth front-to-back enables real aquascape + tang stocking.4 themed setups90-gallon stocking ideas90g (48"x18"x24" or 36"x18"x30") is a step up from 75g - more vertical for aquascape, deeper sump options.4 themed setups125-gallon stocking ideas125g (72"x18") opens up large oddball + tang school + premium reef builds. The 6-foot length is a major upgrade from 4-foot tanks.3 themed setups180-gallon stocking ideas180g (72"x24") is show-tier reef + adult oddball. The 24-inch depth is finally enough for proper aquascape on a 6-foot tank.2 themed setups

Aquarium-keeping fundamentals

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.

Frequently asked questions

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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