I have a Rainbow 320 in line chlorinator. It already has a check valve incorporated in the bottom of it. Pool guy told me today I should have another check valve installed in the plumbing line between the chlorinator and heater to ensure chemicals do not flow into heater. After thinking about it it struck me as odd since he installed the heater to begin with and did not mention it at the time of install. Is the Rainbow 320 built in check valve sufficient or is a secondary check valve warranted? Have not had any issues with heater in 2 years since install. Thanks for your input.