When calcium chloride hexahydrate dissolves in water, the process is endothermic, meaning it absorbs heat from the surroundings.
Calcium chloride hexahydrate absorbs 31 btu/lb.
31/21 = Temp drop of 1.5 degrees for 1 lb in 2.5 gallons of water.
Calcium chloride tetrahydrate is only slightly exothermic (25 btu/lb).
25/21 = 1.2 degrees temp increase for 1 lb in 2.5 gallons of water.
It's possible that if there really was very little or no temperature rise, the calcium might have been one of these compounds or maybe something else.
Calcium chloride hexahydrate absorbs 31 btu/lb.
31/21 = Temp drop of 1.5 degrees for 1 lb in 2.5 gallons of water.
Calcium chloride tetrahydrate is only slightly exothermic (25 btu/lb).
25/21 = 1.2 degrees temp increase for 1 lb in 2.5 gallons of water.
It's possible that if there really was very little or no temperature rise, the calcium might have been one of these compounds or maybe something else.