How do you keep a garden pond scum free?

Factual Questions
1

Since we want fish at some point chlorine is out, it does have a pump in it for a mini waterfall effect but that doesn’t seem to have stopped bacteria from spawning as now when the pump’s on a layer of foam forms on the surface.

Anyone know how to get rid of it and stop it happening again without poisoning the water for future fish?

2

Barley straw. Works like a charm, and no harm to fish.

3

Always keep some bail money handy for the garden pond scum.

(Other than that, I have heard good things about the barley straw mats, but I have no experience with them.)

4

Read about foam in a pond here and here. Buy stuff to pour into the pond to get rid of foam here and here.