Check the wiring inside. Electronics might seem interesting but not easy to understand. Take a two way radio and place a flouresant lamp next to it. (Without wires connected) Start talking on the radio and the lamp will glow (but not enough energy to keep your pumps going when ESKOM fails). You can take the same meter that you used to test he pond and stick the 2 probes in the air next to your TV ( Not plasma) and you will be surprised about the magnetical energy you pick up ( Eskom still sucks since it won't power the pump)
On a more serious point, check your wiring and connections. 200 milli volts might not be much but since you have a problem with the easy, it will be good to get feedback from you. You never know, someone else might have a similar problem in the future

I removed the 0.45 pump on sunday and borrowed another one from my dealer while mine is in for a repair/service.

Then i noticed that i still had a 0.1 ACV in my pond!

It turned out that my terminals of my one 33w UV light was slightly wet and this was causing it. I did not pic it up as i was switching the UV lights on and off at the same time as the faulty pump. Im now wondering if the pump was faulty....hmm well tolate now its already at speck. I think the O-ring on the UV was leaking slightly but not so much that i would notice. I hanged the termnals out to dry and the problem has disappeared since then.

So at the momment my pond is perfect.

Thanks for feedback Wayne. I am sure this can happen to anyone and a small problem can cause big trouble. In my old pond I had an open neutral wire going to a small pump. Had a big shock when I wanted to clean the pump. Had no earth leakage on pump.