Identify what you're looking at
| Looks like | Probably |
|---|---|
| Brown dust on sand/glass in a new tank | Diatoms |
| Long green strands you can grip | Green hair algae (GHA) |
| Fern-like, feathery, dark green, hard to pull | Bryopsis |
| Shiny green balloons/bubbles | Bubble algae (Valonia) |
| Red/maroon slimy sheet with bubbles | Cyanobacteria |
By type — and how to beat it
Diatoms (brown dust)
Almost universal in new tanks — silicates plus a young system. Usually harmless and passes on its own in a few weeks as the tank matures. A cleanup crew and patience is all it needs.
Green hair algae
Driven by excess nutrients and light. Control the fuel: get nitrate and phosphate into a sensible range, manually pull what you can, add hungry grazers (snails, hermits, some tangs), and don't overfeed.
Bryopsis
Tougher than GHA and most grazers won't touch it. Raising magnesium to ~1600 ppm with a specific product for several weeks is the classic treatment; Fluconazole is another route many reefers use. Nutrient control still matters.
Bubble algae
Remove carefully by hand — try not to pop the bubbles into the water, which can spread it. Emerald crabs help keep it in check.
Cyanobacteria (red slime)
Technically a bacteria, not algae. Tied to excess nutrients, low flow, and detritus. Increase flow, siphon it out, improve nutrient export, and it recedes. (Its opposite twin, dinoflagellates, needs the reverse — raising nutrients.)
The one habit that prevents most of it
Nearly all algae traces back to nutrients and consistency. Keep nitrate and phosphate in a stable, sensible band — not zero, not sky-high — and most outbreaks never start. Log them in TankMate to catch the creep early, and snap a photo for an AI read when you're not sure what you're looking at. It's free on Google Play.