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Worst case: Observe and monitor3 possible causes

Snails are taking over

Small snails appear in increasing numbers on the glass, plants and substrate.

Short answer

A snail population is set by the food available, and the food available is set by how much you feed. A snail explosion is an overfeeding signal, and the population falls when the food does.

Check these first, in this order

  1. How much food is going in, and is any left after two minutes?
  2. Is there detritus accumulating in the substrate?
  3. Are the snails actually damaging anything?

Possible causes

Ordered by urgency, then by how commonly each one turns out to be the answer. The discriminator is the observation that separates this cause from the others — use it before acting.

Overfeeding

Observe and monitorvery common

How to tell: Population rose after feeding increased, or food is visible on the substrate.

Check

  • Feeding volume and frequency
  • Whether food remains after two minutes

Response

  • Reduce feeding. The population declines over several weeks without any intervention.
  • Vacuum detritus at each water change.

Snails arrived on new plants

No action neededvery common

How to tell: Appeared shortly after adding plants. Almost universal with plants from established display tanks.

Check

  • Recent plant additions

Response

  • Manual removal, and a blanched courgette left overnight as a trap works well.
  • Rinse and inspect future plants, or quarantine them.

Deliberate introduction of a parthenogenetic species

No action neededoccasional

How to tell: Malaysian trumpet snails were added intentionally. A single individual founds a population.

Check

  • Whether MTS were added

Response

  • Accept them — they are genuinely useful in a sand substrate — and control by feeding less.

    What not to do

    • Copper-based snail treatments, which kill shrimp and can harm scaleless fish.
    • Adding an assassin snail or a loach as a first response — both are permanent additions with their own requirements.

    Prevention

    • Feed conservatively
    • Inspect and rinse new plants
    • Vacuum the substrate regularly