What aquarium size for a beginner
A small tank is harder than a big one. Here's why 100 L is the reasonable minimum.
"What size aquarium should I buy?" is a simple question with a counter-intuitive answer. Not the smallest one you can afford. And not the biggest. Somewhere in between, leaning bigger.
Why a small aquarium is harder than a big one
Buffer principle: the more water, the slower parameters drift. In a 30 L tank, overfeeding causes an ammonia spike within a day. In a 200 L tank — within a week, with time to react.
Likewise: temperature swings less, pH is more stable, the bacterial cycle is more robust. A big aquarium forgives mistakes.
Volume recommendations
Minimum 60 liters
Suits a nano biotope with one betta, a gourami pair and 5–6 rasboras, or a shrimp tank. Less than that is a specialized niche, not for beginners.
Sweet spot 100–150 liters
The most convenient range. Holds several different species, easy to maintain, doesn't require huge furniture.
200 liters and up
You can keep larger fish (angelfish, cichlids) and bigger schools. Water changes are less frequent (every 2 weeks instead of weekly).
The "1 cm of fish per 1 L" rule
An old rule of thumb: total length of all adult fish should not exceed tank volume in liters. For example, a 100 L tank — 100 cm of fish.
It's approximate. Adjustments:
• For active species (barbs, danios): divide by 2 — they need room.
• For large "messy" fish (goldfish, cichlids, plecos): divide by 3.
• For peaceful small fish (neons, rasboras): multiply by 1.2 is fine.
How to count "useful" volume
From the advertised liters, subtract substrate (10–20 %), decor (5–15 %), and headroom (5–10 %). A "100 L" tank holds 70–80 L of actual water.
Length vs height
Fish swim mostly along the length. A long, low 80×40×30 tank is better for active fish than a 50×50×50 cube of the same volume.
A tall tank is needed for angelfish (50+ cm depth) and for biotopes with floating plants.
If choosing between two sizes — take the bigger one. Aquarium-keeping is a decades-long investment, and 100 L vs 60 L is a small price difference but a huge difference in maintenance comfort.
FAQ
- Can a betta be kept in 5 L?
- Technically yes, but it conflicts with modern aquaristics ethics. The minimum for one betta is 20 L with a heater and filtration.
- Is a round bowl suitable?
- No. It distorts the fish's vision, doesn't hold enough volume for proper filtration, and direct sun from any side triggers algae.
Goldie editorial team
Practising aquarists with a combined 30+ years of experience · Biologists and editors, fact-checking against FishBase and Seriously Fish · Every piece is reviewed by a qualified ichthyologist before publication
Scientific board — ichthyologists and veterinarians
Ichthyologists and veterinarians with university degrees · Reference FishBase, Seriously Fish and peer-reviewed literature · Sign every reviewed article with their credentials shown
Sources
- Seriously Fish — Stocking guide · Seriously Fish · 2026-05-22