Is green water harmful to fish?
Green aquarium water is not considered dangerous to fish. In fact, many fish happily live in green-colored water in their natural environment. The same goes for plants. While the algae that makes up green aquarium water feeds on many of the same nutrients that your plants do, it shouldn’t cause any direct harm.
What kills green algae in water?
Add 1/4 teaspoon of *bleach to every gallon of water you store – Bleach kills algae and prevents it from growing.
How do I get rid of algae in my fish tank naturally?
Change the water regularly to keep nutrients low and if you have plants, use a liquid fertiliser to actually strengthen the plants and help them to fight off algae naturally. If the tank contains no live plants then you can use nitrate and phosphate resins to soak up those spare nutrients and starve the algae.