Deicers - Thermo 100 W or Laguna 200W?

[backyardponder]

Hi there!
This winter, I was thinking about adding a deicer to keep a hole open in my little pond. Last two winters, I used a air pump and it works for a while.  My pond is about 6x7 ft, only 18 inches deep. AZponds has two deicers, that seem to work for my size pond: Thermo 100W for $39.95 and Laguna 200W for $29.99.
I don't think I need anything with more watts since I only have about 450 gal.
Any recos on either of these?

Thanks!
Eija
(zone 6 in Cincinnati)

[mcp]

Eija, I live in zone 5. Last winter I used a Thermo 100 watt and an air stone. I lost no fish through the winter. Pond is 12x15x3 ft. I plan to use the same system this year.