| What It Is | Normal algae/film stages of a young tank |
| Timeline | Roughly weeks 2–12 |
| Usual Order | Diatoms → maybe cyano/algae → clears |
| The Fix | Patience, consistency, nutrient export |
| Golden Rule | Don’t panic — don’t tear it down |
Overview
Almost every new reef goes through an “ugly phase” — a few weeks where the tank grows brown diatoms, maybe some cyano or hair algae, and generally looks worse before it looks better. It’s normal, it’s temporary, and it’s a sign the tank is maturing. The biggest mistake is panicking and changing everything at once.
What’s Happening
A young tank hasn’t balanced yet: nutrients from the initial cycle, silicates in new rock/sand, and immature microfauna let simple organisms bloom first. Brown diatoms (a dusty brown film on sand and glass) usually come first and often clear on their own as silicates deplete. Some tanks then see a cyano or algae phase before the biology matures and competitors move in.
How to Get Through It
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- Be patient and consistent — stable parameters and time are the real cure; most ugly phases self-resolve over weeks.
- Keep up small water changes and use RODI water (tap silicates feed diatoms).
- Add a modest clean-up crew once there’s algae to graze.
- Don’t overfeed or over-light a young tank — you’re feeding the bloom.
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Common Mistakes
Panicking and changing everything: new light, new media, big dosing — instability prolongs the ugly phase. Scrubbing daily and overfeeding: stirs nutrients and feeds blooms. Chasing zero nutrients: overcorrecting can trigger dinoflagellates — far worse than diatoms. Ride it out.
Related Guides
How to Cycle a New Saltwater Aquarium · How to Beat Hair Algae (Green Hair Algae) · How to Get Rid of Red Slime (Cyanobacteria) · How to Beat Dinoflagellates (Dinos)