Since phosphate reactors are fluidized beds they are best operated under the point of fluidization. That being said, get a pump that allows you to control flow. Once installed turn the pump on with a very low setting and adjust up until you start to see the reactor media start bubble up and move on top of the bed. At this point adjust the valve down so that you can barely see the top of the reactor media bed moving. You have reached the point of fluidizatioin, this is where these kinds of reactors reach their optimum efficiency.