Look at the hash marks on the valves. Also look in the manual, it specifically tells you to use them to vary the flow. All Fluval filters offer this feature
yeah will prob go fluval fx5. my lfs is woking out a deal, for 8 millimetre glass instead of 6, a full support base in the stand ( I want the whole bottom of the tank supported by a solid slab of wood rather than just resting on the edges), and a Fluval Fx5. I think the financal downturn has hit him but, he was saying now i can't sell these for nothing... So we will see.
Yes, the Fx5 has variable flow control valves called "Aqua Stop" valves. They are designed for you to control the flow. I have my Fx5 on a 55 gallon but I have the flow around 60% most of the time.