How to Use Mosquito Dunks to Eliminate Fungus Gnats

How to Use Mosquito Dunks to Eliminate Fungus Gnats

Fungus Gnats: Fast, Safe Control for Bioactive Setups

Fungus gnats show up when things stay a bit too damp and there’s plenty of food for microbes. The good news: they’re easy to control without nuking your enclosure. Here’s a clean, Canadian-friendly guide to shut them down fast—and keep them away.

Watch: Fungus Gnats Fix (Step-by-Step)

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Quick answer at a glance

  • Cause: Consistently wet top layer + extra organics (leftover food, algae, fungus).
  • Fast fix (3 steps): Let the top 1–2 cm dry → reduce feeding → add spot treatment (see Bti notes below).
  • Prevention: Good airflow, dry “cap” layer on top, tiny portions of food, and regular spot-cleaning.

Enclosure & substrate

Gnats thrive in persistently wet, low-airflow spots. Keep the top layer drier and the air moving.

  • Base: A balanced mix like Tropical Soil supports bioactive life without turning swampy—if you let the surface dry between waterings.
  • Top “cap” layer: Add a thin, dry cap (1–2 cm) using Arid Soil to discourage gnat egg laying at the surface.
  • Ventilation: Use a lid with decent airflow; add extra vents if the surface stays shiny or clammy for days.

Feeding & diet habits (the real gnat lever)

  • Tiny portions win: Offer small amounts that are fully consumed within 12–24 hours.
  • Clean protein, sparingly: A pinch of Pill Diet (Small) 1–2× per week is plenty—don’t overdo it.
  • Spot-feed on a dish: Present food on a leaf or small tray so leftovers are easy to remove.
  • No buried food: Don’t push food into the substrate—microbes + moisture = gnat nursery.

Water & humidity

  • Dry the top: Let the top 1–2 cm dry out completely between waterings/mists.
  • Moisture zoning: Keep one small retreat moist, leave the rest on the dry side so custodians can choose.
  • Avoid constant misting: Choose fewer, deeper cycles over frequent spritzing that keeps the surface perpetually damp.

Behaviour & ID

  • Adults: Tiny black flies hovering or running across the substrate and glass.
  • Larvae: Thin, pale, wormlike; feed on algae, fungi, and decaying organics in the top layer.
  • Cycle: Quick—so fixing surface moisture and food exposure for even a week can break the loop.

Cleaning & maintenance

  • Leftover sweep: Remove uneaten food within 24 hours; wipe algae from glass.
  • Surface refresh: If a patch stays soggy, scoop and replace the top 1 cm with fresh dry mix; re-cap with Arid Soil.
  • Sticky traps (optional): Use a small piece above the enclosure to catch adults; keep adhesive away from animals.
  • Bti (mosquito dunk) method: Soak a small chunk in water; use that water to lightly moisten substrate only where needed. Avoid drenching the whole enclosure—target the problem area.

Troubleshooting

  • Still seeing adults? You’re close. Dry the top completely for a few days, feed less, and refresh the cap layer.
  • Gnats return after waterings? Water more deeply but less often, and only one area at a time—rotate.
  • Houseplants nearby? Treat any potted plants in the same room; they can be the source.

Shop the gear in this guide

  • Tropical Soil — balanced base that won’t swamp out if you let the surface dry
  • Arid Soil — dry “cap” layer to discourage egg laying
  • Pill Diet (Small) — clean, balanced feeding with fewer leftovers

Questions about your setup? Pop into our Discord or message @incoginverts on Instagram—happy to help dial it in.

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