What would be great is if I can find an actuated butterfly valve to minimize the ramp time. That may be a separate DIY project using a standard valve with an external (dry) solenoid actuator. I expect the force required to make that work would be quite large.
The commercial ones are so expensive, I might as well buy a Tunze powerhead
http://viewer.zmags.com/publication/...#/d4e3ccef/204