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's built-in check valve sufficient to protect the heater or is a secondary check valve needed? I have not had any issues with heater in 2 years since install and the prior heater. Thanks for your input.