why o why is my pond so green?

Brief：
i have followed all advice given to me by my local fish supplier. and yet my pond is green. any one know what to do. i have tried all the chemicals. i.. 

i have followed all advice given to me by my local fish supplier. and yet my pond is green. any one know what to do. i have tried all the chemicals. i cant afford a ultra violet light box.

Is your pond fairly new? This does happen until it finds the right balance. It generally settles with time.Don't be tempted to change the water!! Its very frustrating.Its all down to algae.Pond Algae comes in many different forms, even different colors (green algae, red algae, brown algae). The two kinds of pond algae frustrating backyard pond owners most often, though, are "green water algae" and "string algae" (also called "blanket weed" or "hair algae")

Green pond water algae are single cell plants that can make the pond look like “pea soup”. These plants are so tiny that they can pass right through a pond filter. Consequently additional forms of control have to be used. Algaecides are not a good choice in the garden pond or water garden, because they will also harm pond and aquatic plants.

It is very important to balance the pH in the pond (it should be between 6.8 and 7.4). Nothing in the pond will be very successful until this first step is taken. Easy to use test kits are available to measure the pH.

Once the pH is balanced one can introduce beneficial bacteria and lots of aquatic plants to compete with the algae for nutrients in the pond and hopefully starve the green water algae. (It is important not to clean the pond filter with chlorinated tap water - this will kill the beneficial bacteria).