Turning green means that your tank has an algae problem. There are several different types of algae, and at least a couple ways to interpret “fish tank turns green” but ultimately the process to fix it is going to be similar. read more
If the aquarium receives any direct sun light, it can cause an algae bloom. If not, you should operate the aquarium light 10 or 12 hours a day, that is provided it's a regular aquarium light not of the high intensity variety. Fast growing floating plants will help control algae by using up the nutrients and providing some shade. read more
In severe cases, the water may be so green that the fish are not even visible. Causes. Excess light, especially direct sunlight. Like other plants, algae photosynthesize light. An aquarium in direct sunlight is more prone to an algae bloom. Too many fish, leading to too many organic wastes that provide nutrients for the plants. Overfeeding. read more