23 Degrees is too warm?

My backyard skating rink simply will not freeze solid. I had built it a few weeks ago, following a design I found online, and have been waiting somewhat impatiently for the weather to turn cold enough for the water in the rink to freeze. W. is so looking forward to lacing up his skates, and to playing hockey in his backyard, but even though the top layer of water has frozen over, the bottom layers will not drop below 34 degrees (during the middle of the night.) Once the sunlight hits the rink, the water warms up to the mid-40s. I realize it’s nearly the end of January, and we’ve gotten hardly any snowfall, and the ground is nowhere near frozen, and I can hope that next Saturday Phil sees his shadow and February brings prolonged freezing temperatures, but if this rink turns out to be a bust I’m going to have a pretty unhappy family.