Most stock tank de-icers will not operate above 40 degrees and every fish tank heater I have found has a minimum setting of 60 degrees. A 60 to 90 degree temperature differential will cause significant evaporation. If that is something you are worried about, closed cell foam floating on top of the tank or bucket will stop it. Bird bath de-icers are no where near 750 watts but even if they were they are temperature controlled and will not heat above 40 degrees.
As far as sealing a hole made in a fount, I tried everything I could think of and could never get a seal that would hold. That's why I went to buckets with nipples. In addition to the fact that founts are just a royal pain in the rear. I cut mine up to use for flashing. For that, they work great.
As far as sealing a hole made in a fount, I tried everything I could think of and could never get a seal that would hold. That's why I went to buckets with nipples. In addition to the fact that founts are just a royal pain in the rear. I cut mine up to use for flashing. For that, they work great.