Calcium chloride hexahydrate solubility limit is 279 grams per 100 ml of water (cold water) in hot water the limit is 536 g per 100 ml water (CRC handbook). I'd suggest you stay below 250 grams per 100 ml water. This limit means you add 250 grams to 100 ml water, NOT that you add 250 grams THEN add water to a total of 100 ml. The container will get very HOT, I suggest you use a glass container and be ready in case it boils over just from the heat of dissolution.