I have two different generation Reeftek reactors on different systems. I've had this problem from time to time as well.
Here's one thing that I did that seems to help some. I put a ball valve at the end of the effluent line and run the ball valve almost totally closed. In other words, the ball valve is just barely open. This allows me to open up the gate valve that comes with the reactor more which seems to provide a bit more pressure on the effluent line, keeping the drip rate more consistent.
Also, make sure that you release any air bubbles at the top of the inside of the reactor chamber. Any trapped air will cause problems with pressure inside the chamber. Make sure that your feed pump is not anywhere near micro bubbles. I had this problem and relocated the pump in a very stagnant area of my sump and it seems to prevent air bubble build up in the chamber.
Jorge has recommended to me as well to try using a dosing pump. I just might do that sometime.