Stocktank deicer failure

When the severe cold snap hit us the deicer failed and I didn't notice
since I run it at night. This was the third year for it and I thought
maybe I should get a replacement but didn't. The pond is very clean but
until I see fish I will worry. This morning I did buy two. The deicer
is thru the ice but the old one is still frozen in with the wire guard
which I need so I don't put a hole in the liner. The goldfish were
getting about 7" or so and really visable from the house. Nothing like
surprises.