Use aquarium heater in pond?
 

Can I do this? got a couple of spare 100Watt heaters
that I used in my indoor aquariums.
Its winter here in the UK and I'm a bit worried about my
pond fish.got 5 golden orfe's and 3 regular goldfish in it.
The pond is approx 40 gallons with a pump/filter setup,
and is above ground level.
Thanks.

John