In home aquariums, many fishkeepers often encounter a common issue — green water.
When the water in a fish tank turns green, it not only spoils the beauty of the aquarium but can also make the fish more prone to diseases, and in severe cases, even lead to death.
To deal with green water, many aquarists tend to use the simplest and quickest method — changing the water. Unfortunately, this approach is often ineffective in the long run.
So, why does fish tank water turn green? And what can you do to solve this problem once and for all?
Let’s dive into the details.
Main Cause: Algae Overgrowth
The fundamental reason for green water in aquariums is the massive reproduction of microalgae (such as green water algae) in the tank.
There are four main factors that cause algae to grow excessively in fish tanks:
1. Excessive Light Exposure
Experienced fishkeepers know that algae, like all plants, require light for photosynthesis.
If your aquarium receives too much direct sunlight, or if the tank light stays on too long or has too high a wattage, algae growth can quickly get out of control.
2. Nutrient-Rich Water (Eutrophication)
When leftover fish food, fish waste, dead fish, or decaying plant matter accumulate in the tank, they release nutrients such as nitrogen and phosphorus.
These nutrients serve as an excellent food source for algae, promoting their rapid growth and turning the water green.
3. Poor Filtration System
If your filtration system is too weak, or if the filter media is not cleaned regularly, waste and debris will remain in the tank.
This not only degrades water quality but also provides the perfect environment for algae blooms.
4. Infrequent Water Changes
Failing to change the water regularly allows waste and nutrients to build up over time, creating a nutrient-rich environment that encourages algae growth.
Once you understand these causes, controlling algae growth and solving the green water problem becomes much easier.
Here are some effective methods to restore crystal-clear water in your aquarium:
1. Control Light Exposure
Place your fish tank in an area with limited direct sunlight and reduce the duration of artificial lighting.
In most cases, 6–8 hours of light per day is sufficient.
Also, make sure to use aquarium lights with the appropriate wattage for your tank size.
2. Feed Fish Properly
Feed your fish only once or twice a day, and only what they can consume within two minutes.
Overfeeding leads to excess food waste and fish feces, both of which release nutrients that feed algae and turn the water green.
3. Maintain an Efficient Filtration System
Ensure your filter has sufficient flow capacity and clean the filter media regularly.
A well-maintained filter can effectively remove waste and keep the water clear.
4. Change Water Regularly
Perform partial water changes once a week, replacing about one-third or one-fourth of the total water volume each time.
Avoid changing all the water at once, as it may stress your fish.
5. Add Algae-Eating Species and Plants
Introduce algae-eating fish or snails, such as Otocinclus catfish and apple snails, to help naturally control algae.
You can also add floating plants like duckweed or water wisteria, which absorb excess nutrients and block sunlight from reaching the algae.
By following these five key steps, you can effectively prevent and eliminate green water in your fish tank, keeping your aquarium clean, healthy, and visually stunning.
