Tank setup

Nano aquariums: a realistic guide

A nano tank is not a small version of a big tank. It is a different system with a much shorter time constant.

2–5 gal / 8–20 LMaintenance planWhat to log
Volume
2–5 gal / 8–20 L
Typical footprint
12–16 in wide, rimless or cube
Water change
30–50% weekly, sometimes twice weekly
Temperature
Stable room temp + small heater
Filtration
Sponge filter, low flow is safer
Best for
Shrimp, snails, one small fish

Nano tanks are the fastest-growing segment of the hobby for good reason: they fit on a desk, cost little to run, and look excellent planted. They are also the tanks where “I tested last week” is genuinely too long ago to be useful.

Why parameters move so fast

  • Evaporation: a litre lost from a 12-litre tank is a ~8% change in everything dissolved in it.
  • Temperature: 12 litres follows room temperature within an hour or two.
  • Ammonia: one missed feeding in a nano tank is a measurable spike the next morning.
  • pH: low KH plus a small volume means a pH crash can happen in a weekend.

The nano routine

CadenceTask
DailyCheck temperature, top off with dechlorinated water, one feeding
Every 2–3 daysTest ammonia in a new tank; test nitrate in a stocked one
Weekly30–50% water change, siphon, glass clean, filter flow check
MonthlyRinse filter media in tank water, inspect heater, check KH
Top-offs are not water changes

Adding water to replace evaporation restores the level and nothing else — the minerals and nitrate stay behind and concentrate. Log top-offs separately from water changes so the two do not get confused in your history.

What nano tanks are good at

Shrimp colonies, a single betta, a planted cube with chili rasboras, and any setup where you want to watch one small ecosystem closely. What they are bad at: fish that grow, fish that need length to swim, and any stocking that assumes a bigger filter than the tank can hold.

Questions

Frequently asked

How small is too small for fish?
Below about 10 litres, most fish are a poor fit — the tank cannot buffer waste or temperature, and swimming space is gone. Shrimp and snails are the honest answer at that size.
Do nano tanks need a filter?
Yes, unless you are running a genuinely Walstad-style heavily planted setup and testing daily. A small sponge filter costs little and gives bacteria somewhere to live.
How often should I test a nano tank?
More often than a big tank: at least twice a week while it is new, and every water change once it is stable. Log each reading — the trend is the useful part.
Keep reading

5-gallon tank

A 5-gallon is a nano tank with no margin for error. What to stock, how often to change water, and the parameters that move fastest at this size.

Read →

10-gallon aquarium

The most common first real tank. Stocking plans, a maintenance schedule that works long-term, and the two parameters that decide whether it stays easy.

Read →
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