I left the fish in their indoor pond after the outdoor pond renovations, as
it was too cool to move them back outdoors. But since the pond is in a cool
part of the basement (entryway), the water is down to 52° now. Making the
room warmer is not really an option, at least not in the short term. So I
plan to use their outdoor heater (newly replaced) to keep them at 68° or so.
But I was thinking that a hot tub blanket might make this more feasible and
reduce my heating costs.

I was looking at this one:
http://www.spadepot.com/shop/Floatin...kets-C637.aspx

But this presents a minor problem for filter return and feeding. If I leave
a large hole for the filter return to drain into will this be sufficient
aeration? Any chance these blankets are treated with bactericide?