So to agree with everyone else, it is completely normal for the ice to crack when you resurface for the exact reason Matt said. However, the issue here is not warm water vs cold ice, it's the fact that you only have a half inch of ice in that area. It's difficult to add "height" to solid ice, as the water will likely get under your slab and not sit nicely on top where you want it to be. But you can add it in thin layers so that it's at least skateable. Just know that I typically recommend at least 3" of ice to support an adult.
Our "measure your slope" article talks about starting at your highest corner. However, if you know the highest point within your rink boundaries are in the middle somewhere, next year you'll want to fill until that section has 4" of water. It may meant extra board height (measure your slope from that bump, not from a corner), but if you can get 4" on top of that bump then you know you'll have plenty everywhere else and you shouldn't run into this issue. Consider this the learning experience for this year. Each year we learn something new, even after several years...so next year you'll know to keep filling!
I'm Joe from Backyard-Hockey.com and EliteRinks.com.
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