Algae fix guide
Brown Algae (Diatoms)
Also called diatoms, silica algae, new tank brown algae
A brown dusty coating on a new tank that wipes off with a finger.
By Mike Elmira
TL;DR, Brown Algae (Diatoms)
Brown algae, really diatoms, is the brown dusty film that coats the glass, plants and substrate in the first weeks of a new tank. It is harmless and almost a rite of passage. It feeds on the silicates and ammonia of a fresh setup, and it fades on its own as the tank matures and those settle. You can wipe it off easily, and otocinclus and nerite snails graze it happily. If it shows up in an established tank, check for a source of excess silicate or a stalled cycle.
How to spot it
A soft brown or tan dust over every surface, thickest on the glass and slow leaves. It wipes away with a fingertip and does not cling like green spot.
What causes it
- A new tank still cycling, with silicates and ammonia present
- Low light in the early weeks
- Occasionally, high silicate source water in an established tank
How to fix it
- Give it time, most new-tank diatoms clear on their own within a few weeks as the tank matures.
- Wipe the glass and gently rinse affected leaves during water changes.
- Add otocinclus or a nerite snail, they graze diatoms enthusiastically.
- In an established tank, check whether your source water is high in silicate.
Keep it from coming back
There is not much to prevent on a new tank, it comes with the territory. Letting the tank mature fully before adding a big bioload keeps it brief.
What eats it
A clean-up crew won’t fix the cause, but these species graze it and keep the last of it down:
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Will brown algae go away on its own?
Usually yes. In a new tank diatoms fade within a few weeks as it matures and silicates settle. A few otocinclus or a nerite snail speed it along, and wiping keeps the glass clear in the meantime.
Why is brown algae in my established tank?
In an older tank it often points at high silicate in your source water, or a stalled cycle after a filter clean. Check both, and the diatoms usually clear once the cause is sorted.