What is a bacterial bloom in aquariums?
A bacterial bloom happens when heterotrophic bacteria multiply rapidly in the water column, giving the aquarium a cloudy or milky appearance.
Why bacterial blooms occur
Bacterial blooms are commonly caused by:
- Newly established aquariums
- Excess organic waste
- Overfeeding
- Disturbing substrate or filter media
These bacteria consume dissolved organic compounds rather than efficiently processing ammonia.
Is a bacterial bloom harmful?
In most cases, bacterial blooms are not directly toxic, but they can:
- Reduce oxygen levels
- Stress fish in severe cases
- Indicate excess waste or imbalance
Low oxygen levels are the main risk during intense blooms.
Bacterial bloom vs ammonia spike
- Bacterial bloom: cloudy water, often stable test results
- Ammonia spike: clear water with elevated ammonia or nitrite
Water testing is the only reliable way to distinguish them.
How long bacterial blooms last
Most blooms resolve naturally within:
- A few days to two weeks
As biological filtration matures, bacterial populations stabilize.
How to manage bacterial blooms
- Avoid excessive water changes
- Reduce feeding
- Increase surface agitation with proper filtration or an Air Pump
- Allow the aquarium to stabilize naturally
Bacterial blooms are common in new tanks and usually temporary.