Do you know your pH? If it's been low, you could be removing copper from your heater. I also wouldn't be surprised if some of the other products have copper in them. Copper is also likely to build up in the pool (until it comes out on your hair).

Your agent may not be lying to you but the truth is screaming in pain. If (s)he's been testing your water and advising you and (s)he let your pH go low enough to take copper from your heater (as suggested), then either way that agent has caused you green hair.

Can you trust that?

I can tell you this: the method of poolcare described here and at pool solutions.com is easy, effective, and relatively inexpensive. It is also liberating - you will be in charge of your own pool with no one to mislead you.