FISH DYING AND BREATHING HEAVY

[reefcat]

So on another thread i was reading about some one who had added new powerheads and his fish started dying, same thing has happened to me when I added 2 new powerheads, all parameters are fine so I thought it was just a bit of sediment that the powerheads had stirred up because there was a bit of a film on the top of the water. But in the thread some one said that there is a harmful coating on some powerheads and I should run them in vinegar and water, I'll do that but in the mean time can I set up my new skimmer without there being a coating problem??!! HELP PLEASE!!
I have done about a 40% water change since all this started.