Veg to Flower???

I am getting ready to switch to flower and I am wondering if there is something I have to do before or when I switch them over? I am running a hydro setup with the ebb and grow system. Didnt know if I have to flush or just do a res change with flower nutes?

THANKS!

Anyone? I want to switch to flower by Sunday.

I am also wondering when I should switch the light? Morning when it first comes on? Or at night when it goes off?

I dont do hydro myself .. but the grows I have watched seemed to clean out the res. then put the flowering nutes in - as for when to start the 12/12 light cycle ... I always set the timer when the lights where on so I could see it , but in my set up its pretty damn dark when the lights go off - not sure if this is correct or not ... If I ever had a negative effect from it - it wasnt enough to catch my attention ..