Clear tea-coloured or amber water is commonly caused by tannins released from driftwood, catappa leaves or other botanicals. Tannins are not the same as suspended dirt and are intentionally used in some blackwater aquariums. If the water is brown and murky, however, test water quality and inspect for decomposing waste, dirty substrate or filter problems.
The word 'brown' can describe two very different tanks: crystal-clear amber blackwater, or a murky aquarium full of suspended waste. A white-cup test quickly helps separate them.
Tannin-stained water
Driftwood and botanical materials release dissolved organic compounds that colour water from pale yellow to deep brown. The water can remain visually clear even though it is strongly tinted.
Many fish from blackwater habitats naturally encounter tannin-rich water, so colour alone is not a reason to panic.
When brown water is actually dirty
If the sample contains particles or smells foul, investigate uneaten food, decaying plants, disturbed substrate, poor mechanical filtration or a neglected filter.
Test ammonia and nitrite because decomposing organic matter can create a water-quality problem.
How to reduce tannin colour
- Perform regular partial water changes.
- Pre-soak or boil suitable driftwood before use where practical.
- Use fresh activated carbon or another appropriate chemical media if you specifically want clearer water.
- Remove or reduce botanicals if they are the intentional tannin source.
Do not confuse tannins with an emergency
Tannins can alter appearance without making the water unsafe. Use test results, fish behaviour and smell to judge the system rather than colour alone.
If fish are gasping, lethargic or showing other distress, treat that as a separate warning sign and check the water immediately.
Related aquarium tools and guides
Frequently asked questions
Are tannins bad for aquarium fish?
Not inherently. Many species tolerate or prefer tannin-rich water, although chemistry and species requirements still matter.
Will carbon remove brown colour?
Activated carbon can reduce dissolved tannin colour when used and replaced appropriately.
How long does driftwood stain aquarium water?
It varies widely by wood type, size and preparation. Some pieces release tannins for weeks or months.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.