Restricting Pump Inflow
 

I have always been told never to restrict the pump inflow but instead restrict the pump outflow to avoid possible damage to the pump if you need to reduce the flow of your pump. However, I just purchased a new Reef Octopus Pellet Reactor and it comes with a valve that you put on the intake of the pump to control how much flow goes through the reactor. Your thoughts? How low can I turn it?

Putting the valve before a pump can lead to a pump running dry and cavitation. This is more of a concern when you completely shut the valve. While your configuration isn't ideal, I think you should be fine as long as you don't shut it off or get really close to shutting it off. Most aquariums pumps don't have a high enough inlet suction pressure to create much cavitation, so you can probably go fairly low, but if it does start cavitating, you'll hear it real quick.

No way to swap the valve position?

Unfortunately, it's one of those new Space Saving models where the pump fits underneath the reactor and feeds right into the body of the reactor. Without a bit of DIY it wouldn't be possible and then it might start taking up more room in my sump which I just don't have.

Then I wouldn't worry about it. Just don't close the valve completely and listen for noises when you turn it down low.

Cant be true! I would never restrict the inflow of any pump.... the outflow shouldnt be a problem though.