Algae control

I definitly believe its the fish that are the problem, lets face it most garden ponds are overstocked, otherwise we wouldn't see our fish much of the time.
The fish waste allows the duckweed and blanket weed to flourish.

 

the pond in question has no fish

 

Yep, thats what I'm trying to say

 

Excess nutrient could be from animal or bird poo getting into the pond. Try to strip the nutrient out with watercress or even just let duckweed take over for a bit and keep fishing it out. Eventually you should get the pond back in ballance. Water change is a last resort as you will be starting from scratch and will have to season your pond again.

My re-vamped pond is starting to get a green tinge to the water already but this is to be expected at this stage. Frogs seem quite happy and the black dots in the middle of the spawn are getting noticeably bigger. Managed to get a few water plants in yesterday and a lot of the bigger rocks are in place.