I have a standard plastic ice cube tray-- there are 16 wells, and you pop the ice out by twisting tray in opposite directions. At my last residence, my ice cubes came out in whole cubes; I've just moved, though, and now my ice cubes are break into shards when I try to remove them. What would cause this? Minerality or something else in the water? The speed at which the water is freezing? The refrigerator does run cold, even after I've adjusted the temperature a few times. I'd love to hear your clever ideas on this.