Troubleshooting: Algae and slime
Are these dinoflagellates, and how do I get rid of them?
Brown or golden snotty strands and film with bubbles, on sand, rock and corals. A sign many keepers use: it fades or disappears after lights out and returns in the day.
Last checked . How we check
What should I check first?
- Test nitrate and phosphate. Dinoflagellates are linked to both being near zero.
- Note any recent change that lowered nutrients: new phosphate remover, carbon dosing, a bigger skimmer, heavy water changes.
- Look under a cheap microscope or ask a club member to: different types respond differently (BRS, search summary).
What is most likely causing it?
Most likely first. The order is our reading of how often the sources link each cause to this symptom.
- Ultra-low nitrate and phosphate. Nitrate under about 1 ppm and phosphate under about 0.03 ppm are the trigger figures keepers quote (forum figures, typical, check). BRS links ultra-low nutrient tanks to dinoflagellates.
- A new, sterile tank with few other microbes to compete. A young tank built on dry rock, especially after aggressive nutrient control.
What should I do?
- Stop carbon dosing and remove phosphate-removing media.
- Let nitrate and phosphate rise to measurable levels, by feeding a little more or dosing them carefully.
- Siphon out what you can, and run filter floss or socks that you change often.
- Some keepers add a UV steriliser or use a few days of lights out; these work for some types and not others (BRS, search summary).
- Be patient: expect weeks, not days.
What not to do
- More water changes to clean it up: they lower nutrients further.
- A cyanobacteria treatment: it is a different organism.
When should I get help?
Something dying right now? Go to the emergency playbooks.
Where do sources disagree?
| Topic | What sources say | Our reading |
|---|---|---|
| Blackouts |
| Identify the type first if you can. Raising nutrients is the step most sources agree on. |