WHITE POWDERY MILDEW!!!

This is my first grow and have been fight WPM since the third week of veg. I am in the 5th week of flower and still pops up on some leaves. The stuff is relentless! While in flower i knock it down with a high alkaline water spray, but still it keeps coming back, not bad, but just enough to piss me off.
My question is: When I start a new cycle in the same room will the WPM come back to infect my new crop since it is already infiltrated the room. If i leave the room empty and no lights on for a few weeks, will it just die?
What are my options? I would rather not go through this frustrating ordeal on my next cycle.

It would be a good idea to spray everything down with a 10% h2O2 solution to destroy any spores that may be present...

Then implement an organic Integrated Pest Management(IPM) when the plants are growing...

Like krunch said, spray it down, then fix your environment. Temps and humidity out of line and fluctuating too much is no good.