It was January 10th as a matter of fact. Exactly five weeks ago.
But I have noticed in previous years, that if the conditions aren't exactly right -- whatever they are supposed to be -- the tadpoles seem to stop growing. The twelve or so remaining in the bath seem perfectly happy well, of course, they don't know any different.
I can't imagine that it is because the water is too cold, a problem in a previous year. If anything, the water has been warmer than usual. I've had the filter/fountain pump going for days while it was hot
(40 degrees +) to try and cool the water by moving it and by contact with the air, sort of on the same premise as sweating.
It seemed to help but wasn't enough. Next I rigged up some old shade cloth over the ponds. Had them on there for three or four days until the weather changed.