Thank you for all the replies, very helpful. I wanted to cut down the flow at night, thus a timeswitch and power control would be helpful, plus I might reduce the energy consumption.
Yes the 15year old Tetra pump is power wasteful and new Oase pumps at circa £200 are half the power use at 80w for 8,000 l/h. Perhaps the cost effective solution is to replace the pump, and perhaps put a gate valve that I have spare in the output line. But there would be no time automation.
I was very interested in the comment that putting a restriction on the pump will reduce energy consumption. Is this because as it works harder the back emf rises and thus its resistance?
I spent some time looking for web answers before I asked this question, and I have looked again this morning. You can buy fancy pumps with their own speed controllers (£600 plus) but there is no information on DIY speed control. There are stories from the USA about a triac fan speed controller sold for pond pumps that didn't always work.
You can get fan motor controllers, they are used in a lot of horticultural set ups. About £30, but no clue on how they work. The fans seem to have inductive motors so perhaps I should speak to a UK manufacturer that I have found regarding if they work for pond pumps.
There also appear to be no 250v single phase VFDs as boards or box devices down at the 1amp rate. You can get nice, assembled motor controllers from China but these are around £100 and 10amp. Again, I don't know enough to understand whether they would drive a 'shaded pole' motor (is that a specific type of inductive motor?).
Edited By norm norton on 12/08/2016 14:42:09