Nano tank filters: sponge vs internal vs hang-on

Small tanks are unforgiving. Ten litres of water gives you no buffer, so the filter you pick does more work than any other piece of gear. Here is the honest breakdown of the three styles that make sense for nanos.

Sponge filters: the shrimp keeper's default

A sponge filter is an air pump, a lift tube and a sponge. That is the whole invention, and it has outlived every "improvement" because it does two things perfectly: it never sucks up shrimp fry, and the sponge holds a enormous amount of bacteria. The trade is flow — you will not get glass-polishing currents out of one. For breeding tanks, shrimp tanks and quarantine, start with the bio sponge filter 4-pack and thank yourself later.

Internal power filters: the all-rounder

A small internal filter gives you mechanical, chemical and biological filtration in one unit, with a flow you can aim. The 4-in-1 internal filter is the one we put in most starter kits under 60 litres; the three-in-one built-in filter does the same job for smaller budgets, and the Xiten submersible suits fry grow-outs because its intake is gentle. One rule: if your shrimp are getting pinned to the wall, aim the outlet at glass, not across the tank.

Hang-on filters: when you want the tank floor clear

Hang-on-back filters keep the inside of the tank empty and make media changes a ten-second job. The catch on nanos is that the waterfall flow can be too aggressive for bettas and shrimp. If your livestock prefers still water, skip this style — or baffle the outlet with a sponge pre-filter.

Whichever you pick, do this

• Rinse media in tank water, never tap water — chlorine kills the bacteria you are paying for.
• Keep a pre-filter sponge on any intake. It saves fry and doubles your surface area.
• Size for roughly 4-6x your tank volume per hour in turnover. More is not better; it is just current.