Having a pond creates a soothing feature and a lovely focal point in the landscape. After all the work of designing a pond, building it, choosing plants and fish and allowing the pond to reach a natural balance, it can be a shock to walk out one day and find the water has turned into a murky green pea soup almost overnight. This is commonly called green water and it can be quite a shock when you first see it. But don't fret.
The first thing you need to know is that there is absolutely nothing wrong with your pond. Green water is a perfectly natural part of the pond cycle. When water starts to warm in the springtime and the sun's rays shine down directly, a single-celled free-floating fine algae 'blooms' throughout the water. Although it looks disturbing, the algae will harm nothing and, if your pond is properly aerated and has a good PH balance, it will go away on its own as the water continues to warm.
Thanks and Regards,