In the aquatic environment, when you have green water, this means that you have too high a density of planktonic microalgae or algae chloroplasts. The presence of heat and sun encourages the proliferation of microalgae. If you have a direct light giving on your aquarium, this one is certainly in excess and of this fact it is a source of proliferation of the microalgae. A significant amount of waste, especially in an overcrowded aquarium, can also lead to green water, as the organic waste discharged will promote the development of algae. Be careful not to use too much food, because the food that is not consumed will turn into nutrients for the algae, causing extremely strong algae growth. When the water is green, it means that it is not clean, and a disturbance of the biological balance with a rate of carbon dioxide which increases greatly, making it impossible for the species present to flourish. The aesthetic aspect is also degraded, and it can pose a threat to the species in your aquarium.