IF you look at this link you can see just above the pump there is a valve that will allow you to reduce the flow into the skimmer.
http://www.marinedepot.com/Coralife...ers-Coralife-ES33000-FIPSISNW-ES33000-vi.html
http://www.marinedepot.com/Coralife...ers-Coralife-ES33000-FIPSISNW-ES33000-vi.html