There is already a flow regulator valve on the intake of the GFO reactor....do I still need to add a ball valve?

intarsiabox's post meant that the pump speed can be adjusted. This is beneficial as you are not restricting the pump with back-pressure when you partially close a valve between it and the reactor

the valve on the reactor should be fine, works fine for myself. having some sort of regulator is a must because gfo needs to tumble slowly:)

ok,...thanx.

now as far as engineering do I run the pump before the reactor and push the water thru or after the reactor and draw the water thru?

I would put the pump before the reactor otherwise you may have to prime the pump. Also depending on set up you wouldn't have good control of flow and could starve the pump if was after the reactor.