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Worst case: Act within days3 possible causes

Holes in plant leaves

Small holes appear in leaves, often starting as pinpricks and enlarging.

Short answer

Pinholes in older leaves are the classic potassium deficiency sign. Ragged or chewed edges are something eating the plant, and the difference is visible up close.

Check these first, in this order

  1. Are the holes clean-edged pinpricks, or ragged bites?
  2. Which leaves — old or new?
  3. Are there fish or snails present that eat plants?
  4. What fertiliser regime is in use?

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.

Potassium deficiency

Act within dayscommon

How to tell: Pinholes appear in older leaves and enlarge, often with a yellow halo. Alternanthera and swords show it first.

Check

  • Whether the fertiliser contains potassium
  • Which leaves are affected

Response

  • Dose potassium, either as part of a complete fertiliser or separately

Something is eating the plant

Act within dayscommon

How to tell: Edges are ragged and bitten rather than perforated. Damage appears overnight.

Check

  • Which fish and snails are present
  • Whether damage appears overnight

Response

  • Identify the culprit — plant-eating fish include silver dollars, most large barbs, goldfish and many cichlids.
  • Switch to tough plants such as Anubias, Java fern and Crinum, or rehome the fish.

Old leaves dying back normally

No action neededcommon

How to tell: Only the oldest leaves, while new growth is healthy. Normal turnover.

Check

  • Whether new growth is healthy

Response

  • Trim old leaves. No action needed.

What not to do

  • Dosing a single nutrient in isolation for a long period without reviewing the whole regime

Prevention

  • Complete fertiliser regime
  • Check plant-eating habits before adding fish