How many gallons in your pond, what is the flow rate through your UV clarifier, and how many watts is it? I know you checked the bulb, but if the system is working (as opposed to just being on), you really shouldn't have such green water.
the pond is aprox 1500-1600 gallons the pumpis an oase aquamax eco 16000 pushing 16000 l/ph the bulb in the uv is 11 watt that is the recomended wattage for the oase filtoclear 15000 according to the shop the light is definetly on as for wether its working or not im not sure how i would check that ,the water passes through it, the light is supposed to kill the algae what else is there to check?
the pump is on the bottom of the pond which is 4ft deep the filter sits on the deck aprox 3m from the edge of the pond but the deck is slightly below the top surface of the pond as its a raised pond, 2ft below ground and 2ft above ground if you check my posts you'll see pics of my set up
And if I understood the above explanation correctly, you're not actually pumping the water very high at all. It's the difference in the waterlines that matters. The four feet of water above the pump offsets the weight of the four feet of water between the outlet and the waterline. Hence you have very little static head, and unless your filter or tubing is highly restrictive, you may be running the water past the UV so fast that most of the algae cells survive to reproduce. Rigging a bypass so that some of the water goes around the UV would fix this. Be careful not to decrease the flow through the clarifier too much, though. If you can use a stronger bulb or add another UV source, that would be even better.
i called OASE yesterday and explained my situation to one of the technical staff he couldn't have been more helpfull he reccons that the uv bulb might be faulty even though its lit it may not be working right aparently its not an uncommon problem so their sending me out another bulb to try FOC so i'll put the new one in when it arrives and report back as to weather the greens gone