Naturally occurs in pond water and is not harmful. Algae is a plant which provides shelter and food for your fish. The only down side of Algae is that it’s not attractive and presents an untidy pond. If excess greening occurs, adding more Oxygenating plants will reduce algae growth to an acceptable level. A good bacterial method can be applied. There are quite a few different products on the market. If the Algae becomes stringy (blanket weed) it is best to take this out by hand or remove the stringy algae by twisting a stick through and removing as much as possible.
Check the PH of the water (a PH tester can be purchased from any aquarium) it should be in between 6-8.
Using any Algaecide product in your pond will kill off algae successfully, but does have negative side effects. The plants in the pond will also take up the algaecide resulting in retarded growth or even death. Waterlilies and submersible plants are most effected. There are a number of other natural products on the market that are straight bacteria which will balance the clarity of the water.