I believe what you are seeing is the warmer water is not as able to absorb the gas that is produced in the salt water cell. I don't have a salt water chlorinator but I have been reading about people noticing bubbles in there return lines. Cold water can absorb more bubbles than warm water. Think about how many bubbles escape when you open a warm bottle of soda as opposed to a cold bottle. I don't think it a problem and would not worry about it.