How do i get rid of Algae

We used to have that problem.
We installed a shade above the pond and added a 60Litre external pond filter box, with the water outlet flowing over a rock cascade and the algae was gone in a few weeks.

Algae is an opportunistic grower and needs light and food to grow. There's not much you can do about the sun but you can get lots of floating plants to take away a lot of the light and they will also suck up a lot of the food (fish waste, phosphates, nitrates, etc.), thereby starving off the algae.

Cut back on the amount you feed your fish also. Presuming they are goldfish/koi, the more they eat, the more they poop. Of course, if they are still juvenile, they need to be properly fed to avoid stunting their growth. Here is a good feeding chart... http://www.texaskoi.com/Articles/you_might_be_over_feeding_your.htm and for fish under 6", here's a chart of their estimated weight... http://www.geocities.com/Tokyo/4468/weight.html

If water is accessible, you should also do a series of PWC's (partial water changes) which will help eliminate the nutrients in the water column.

I agree with Lenny. You could also try barley balls, you can get them on ebay. Make sure you have plenty of aeration (Waterfall/Bubbler/oxygenating plants). If your pond is full sun like mine,it's something that you'll probably have to fight with. The more plants the merrier. You could use products like tetra pond's algea control, but it won't kill all algea, or a uv light but that will also not kill all types of algea.