"Ian" wrote in message ...
The tadpoles have died, the fish have died. When I switch the fountain on
white froth appears on the surface. Any ideas ?

If the dead fish and tadpoles are still in the pond and decaying then your
fountain is acting as a Protein Skimmer, think of the froth on a beach.
You need to drain and clean out the pond completely, it won't be pleasant!
You will then start with a clean sheet and I would suggest you get hold of a
good water quality test kit (Tetra) and test the water ,say, monthly
especially in spring next year to see if it was a water quality problem that
killed the fish/frogs.

Alternatively it may have been a disease, possibly brought into the pond by
the frogs, if so there is a chance it will all happen again next year. Or it
might be a parasitic bloom, Costia does this sometimes in the spring with
devastating results (I speak from experience!) the fish basically suffocate.

I am assuming you haven't done anything silly like feeding the fish too soon
in spring (when water temp under 50°F) or when there are nice juicy tadpoles
to eat so that uneaten food pollutes the water.
You did clean out the pond in the autumn didn't you?

--
Regards
Bob

Some photos of my plants at.....