How to know it's dinos
Dinoflagellates look like brown, tan, or golden snot or stringy webs, usually with trapped air bubbles, coating rock, sand, and glass. The giveaway: they often appear during the day and largely disappear overnight, then come back. If you're wiping the same brown slime off every morning, it's probably dinos, not ordinary algae.
Why they show up
Dinos thrive when the tank is too clean. Nutrients bottomed out to zero — nitrate at 0 and phosphate at 0 — wipe out the algae and bacteria that normally out-compete them, leaving an empty lane dinos race into. Newer tanks with immature biology are especially prone.
The counterintuitive fix: feed the tank
The core move is to bring nutrients back up so healthier organisms can crowd dinos out:
- Raise nitrate to ~5–10 ppm and phosphate to ~0.05–0.1 ppm — dose them if needed, or simply feed more.
- Stop the over-cleaning: back off aggressive skimming, filter media, and water changes for a while.
- Add biodiversity — a bottle of quality bacteria, or a cup of sand/rock from a healthy established tank.
Knock down the population while you rebalance
- UV sterilizer. One of the most effective tools — many dinos go planktonic at night, and a UV unit kills them in the water column.
- 3-day blackout. Dinos need light; cover the tank fully for ~72 hours (corals tolerate it).
- Manual removal. Siphon them out daily through a filter sock so you're exporting, not spreading.
Beating dinos usually takes a few weeks of consistency, not one silver bullet. Don't panic-swing everything at once.
The key number to watch
Since dinos are a nutrient problem in reverse, the fix lives or dies on keeping nitrate and phosphate up and stable — not chasing zero. Log both in TankMate so you can hold them in the target band while you clear the outbreak, and snap a photo for an AI read if you're not sure it's dinos versus another algae. It's free on Google Play.