HELP!!! Green water in fresh water fish tank!!?

We have a 10 gallon fresh water fish tank which we have had since December. We have several guppies and an algae eater in the tank. There have been no problems until now. In the last 2 weeks, the water has turned very cloudy and green. The water is testing fine by both our strips and the store's tests. We... show more We have a 10 gallon fresh water fish tank which we have had since December. We have several guppies and an algae eater in the tank. There have been no problems until now. In the last 2 weeks, the water has turned very cloudy and green. The water is testing fine by both our strips and the store's tests. We have performed 40% water changes every 3 days at the suggestion of the store where we purchased the tank. We started to use a tap water conditioner and "Cycle" with every water change, but nothing is working. It is not in direct sunlight, we are very careful with the feedings and we have vacuumed the rocks and cleaned the glass and plants with each water change. We have a carbon filter in the tank and a heater. My daughter is upset she can no longer see her fish and, quite frankly, it looks disgusting. I have followed all of the suggestions given with no success. Anyone got any new ideas?
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