Cleaning sand is different from cleaning gravel — you hover the vacuum just above the surface rather than pushing it in, so waste lifts away while the sand stays put. Done right, a sand substrate stays clean and never traps harmful gas.

Here is the technique.

The technique

1. Hold the gravel vacuum 2–3 cm above the sand, not buried in it. Waste (mulm) is lighter than sand and lifts into the siphon while the sand falls back.

2. Move slowly across the surface, section by section, during your weekly water change.

3. Gently stir deep areas under decor with your finger or a chopstick to release trapped waste.

Preventing anaerobic pockets

Sand can compact, creating oxygen-free zones that produce toxic hydrogen sulphide gas (a rotten-egg smell). Prevent this by keeping Malaysian trumpet snails, which burrow and aerate the sand, or by stirring the substrate lightly each month.

What not to do

• Don’t push the vacuum deep into sand — you’ll siphon the sand away.
• Don’t remove sand to “wash” it once the tank is established — you’ll destroy beneficial bacteria.
• Don’t let deep sand sit completely undisturbed for months.

For the full routine, see how to clean a fish tank.

Frequently asked questions

How do you clean sand in a fish tank?

Hold the gravel vacuum a few centimetres above the sand so waste is lifted into the siphon while the sand falls back. Work across the surface during your weekly water change.

Why does my aquarium sand smell like rotten eggs?

Compacted sand can form oxygen-free pockets that produce hydrogen sulphide gas. Prevent this by keeping burrowing snails or gently stirring the sand each month.

Can you use a gravel vacuum on sand?

Yes, but hover it just above the surface rather than pushing it in. Buried, it will siphon away the sand along with the waste.

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— Jaqline Smalling, FishForever