Two days out:
Big farm pond lost 1/4 inch in two days (whut?!?) and rubber-lined pond lost 1/2 inch. So um, early to say, but certainly better than the 1+ inch I would have gotten with no treatment in the big pond, and even better than the 1/2 inch I expected.

The small garden pond water was warmer, so higher evap when the cold weather hit.