Dinoflagellates are unicellular microalgae that can quickly invade a reef aquarium. They often form a brown, sometimes bubbly film, covering live rock, sand, and even corals. Besides their unsightly appearance, some dinoflagellates are toxic to invertebrates and can weaken the balance of your tank.
In this article, Atelier Récifal explains how to recognize a dinoflagellate invasion and what solutions to put in place to eliminate them effectively.
1. Recognizing Dinoflagellates
- Appearance: brown viscous film with air bubbles on the surface.
- Location: on sand, live rock, and sometimes tank walls.
- Behavior: they often disappear at night and quickly reappear with light.
💡 Be careful not to confuse them with simple brown algae (diatoms).
2. Understanding the Causes
Dinoflagellates usually appear due to an imbalance:
- Nutrients too low (NO₃ and PO₄ close to zero).
- Excess light or unsuitable spectrum.
- New water without competitive microfauna.
- Excessive use of phosphate-removing resins.
👉 A “too clean” tank often encourages their appearance.
3. Solutions to Eliminate Them
🔹 Adjust Nutrients
- Maintain measurable levels of NO₃ (2-5 ppm) and PO₄ (0.05-0.1 ppm).
- Avoid aiming for “zero nutrients,” which weakens bacterial and algal competition.
🔹 Reduce Light
- Decrease lighting intensity and duration for a few days.
- Check the spectrum: prioritize blues and reduce whites.
🔹 Strengthen Biological Competition
- Introduce or boost microfauna (rotifers, copepods).
- Use live bacteria to strengthen biodiversity.
- Some detritivores (snails, sea urchins) can help limit their spread.
🔹 Additional Methods
- UV filtration: effective against free-floating forms in the water.
- Efficient skimmer to eliminate toxins.
- Siphon affected areas regularly.
⚠️ Avoid miracle chemical solutions: they mask the problem without treating the cause.
4. Preventing Their Return
- Maintain a balance of nutrients / light / flow.
- Do not over-sterilize the tank water.
- Regularly monitor your parameters.
💡 Atelier Récifal Tip: a balanced reef aquarium with rich microfauna is the best weapon against dinoflagellates.
Conclusion
Dinoflagellates are a nightmare for many reef keepers, but with a good understanding of their origin and a comprehensive approach (nutrients, light, biodiversity), it’s possible to eliminate them permanently.
At Atelier Récifal, we support enthusiasts in managing and succeeding with their reef aquariums.
