I have a commerical heater(what I was told) installed on my Salt Water pool. It heats well but on the cast iron elbows where I have drains or plugs, I have a lot of rust and have had to re tap the threads twice now to get the plugs to thread back in so I can use the heater... Now I am wondering what the inside of the head looks like and is there a possibility that I will get rust in my pool when I start using the heater in a few weeks.

Thank you, 

Jim