04-06-2010, 07:48 PM
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Coincidentally I just did a response to the same question, so for ease I'll just copy and paste it here; it was specific to that situation but the general info is the same. Byron.
Green water is caused when green unicellular algae reproduce so rapidly the water turns green. This happens because of high light and high nutrients.
I would be interested in the exact number for nitrates; I expect it is very high, certainly not "normal" or this would not occur.
The light you have is also contributing to the problem; the "blue/white" I assume is actinic or similar, a type of light that is intended for corals and reef tanks because it simulates the colour of sunlight that penetrates to those depths. It is not a good choice for freshwater, as all algae find it favourable, and plants do not do well under it.
Having a well-planted tank can prevent green water, provided the light is balanced with the nutrients such that the plants can use both completely. But it takes more than a few plants. Without plants, there is nothing to use those nutrients except algae.
A caution on using chemicals to handle algae: don't. These will not work on green water, but even with other types of true algae, they are very dangerous to the fish and not worth the risk. There is always a reason for algae, and finding it and rectifying it is the only good course.
As for getting rid of it, obviously reduce the nutrients and the light. Even if you did reduce this with major water changes, it will only return if the cause is not rectified. What is the fish load in this tank? And what is the feeding schedule? And normally how often is a partial water change carried out, and with how much volume? Knowing this information will help us advise on the solution.