The sea makes the sky blue, but what makes water green? Green water’s technical term is Infusoria. Now that is a very complicated word for something that is actually very simple. Green water is green because it is home to a plethora of many different algae, and other single cell organisms. These minuscule specks of life are green because of the chlorophyll in their structures, and because water is clear if there are enough of these little buggers, your water will appear to be green! It’s as easy as that. If you think about pond water, or swamp water, it is simply that. Those bodies of water are so thick with various plant forms and microscopic life that it appears murky and cloudy.
The real question is, what to do when my water is green when it shouldn’t be or not green when it should be?
When Green is Good
Green water is an ally if you have creatures in your tank that love to feast on microorganisms like Fan or Bamboo shrimp. These shrimp need a good amount of algae to be happy and well fed. Also many fish fry in their week or two after birth need microorganisms like the ones in green water to eat because they are too small to eat any other kinds of foods. Basically you need green water if your tank mates need microorganisms in it for food.
Here is a quick and easy way to culture your own green water.
When Green is Evil
Some people end up with green water in their tank when they don’t need it and that can be a huge problem. Green water in a tank means there is an excess of nutrients and sunlight, which the algae in your tank will use to flourish and multiply. With nothing that will eat these microorganisms they can build up quickly in a tank. Not only is it unpleasant to look at, it can thicken and can cloud your tank to the point where not enough light penetrates the lower areas of the tank, causing the plants and algae in that lower region to die off quickly and in vast amounts. This will affect your ammonia, nitrate, nitrite levels and more. Its 100% an evil villain at this point because this will throw off the nitrogen cycle, make your water parameters go crazy and be hazardous to everything living in your tank.
In order to keep you’re your water clear, you’ll need to do a few things. It is always good to have a few plants in your tank, because they compete with the green water microorganisms in your tank for nutrients. Duckweed is pretty good for this. This will help prevent a ‘baby boom’ of algae in your tank. Limiting your sunlight intake, or shortening it will help a lot as well. Doing regular water changes is vital to keep your water parameters at the proper levels and to dilute the amounts of algae and nutrients in your tank. Also don’t overfeed your tank mates! Anything that contributes to bad water quality will contribute also to green water growth.
Also maybe adding some freshwater clams, Fan Shrimp (if you have fan-friendly tank mates), cute snails (for surface algae, and if you don’t mind waking up to a million snails in your tank), plecos and other bottom feeders (if they, again, will not disturb your other tankmates) will help combat green water.