If you are talking about power heads are you running them on some sort of a controller? Many of these will run backwards when they are switched on and off.
Mike is that what you think the blowers are just cheap or not made for turning on and off I didn't know if maybe I could switch magnets if there's a trick to something to do
I have seen many named brand power heads do this when they are switched on and off. They tend to go in reverse. Might want to contact manufacture about this issue.