Brown/Diatom Algae
A brownish dusty coating, most common in newer tanks -- usually resolves on its own as the tank matures.
Runner-up: Green Spot/Hair Algae · Retake the quiz
Why this fits you
- You see a brown, dusty coating on glass, decor, or substrate.
- Your tank is relatively new (under a few months old).
- This appeared gradually rather than as a sudden bloom.
Brown/diatom algae is extremely common in newer tanks, caused by silicates available early in a tank's life. It typically clears up on its own as the tank matures and silicate levels drop, often within a few weeks to a couple of months, without needing aggressive intervention.
How it compares
| Algae type | Appearance | Typical cause |
| Green Water | Cloudy green water | Excess light, often direct sun |
| Brown/Diatom Algae | Brown dust on surfaces | Silicates in new tanks |
| Green Spot/Hair Algae | Green spots or strands | Light/nutrient imbalance |
| Black Beard Algae | Dark bristly tufts | Unstable CO2/flow |
Buying checklist
- Wipe it off during regular maintenance -- it comes off easily and doesn't require special treatment
- Patience is often the real fix, since it commonly resolves as the tank matures
- Nerite snails and other algae-eating cleanup crew members handle this type well
When this isn’t the right fit
Brown dust is not a safe bet for an established, stable tank that suddenly shows it. Look for a source such as new decor, new substrate or silicates in your tap water, or for old, dying leaves. If the coating is slimy, stringy or spreading fast, it may be something else, so look at it closely before you wait it out.
Other results from this quiz may suit your situation better:
- Green Water (Free-Floating Algae): Cloudy green water from free-floating single-celled algae
- Green Spot/Hair Algae: Hard green dots or stringy green growth
- Black Beard Algae (BBA): Dark, bristly tufts, often on plant edges or hardscape
If your fish or plants show signs of stress or illness, test your water and ask an experienced fishkeeper or an aquatic veterinarian before you treat.
Run the numbers
Frequently asked questions
Why does my new tank have brown algae?
New tanks often have elevated silicate levels, which diatom (brown) algae feeds on -- as the tank matures and silicates deplete, this type of algae commonly fades on its own.
Should I use an algaecide for brown algae?
Generally not needed -- brown/diatom algae is usually a temporary new-tank phase that resolves without chemical intervention; wiping and patience are usually enough.
Do any fish or snails eat brown algae?
Yes -- nerite snails and many plecos are effective at grazing diatom algae off glass and decor.
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