A DC controller that just regulated the voltage would be relatively simple.
I'd like to hear from Don and Scooterman for a more difinitive answer. I also saw these new pumps and was considering making my own controller until I read a few posts suggesting the motors were actually AC.
Quoted from mabviper on RC in a thread that just seemed to die in mid july.
"Anyhow, for those EE guys and girls, you can control these pumps buy designing a controller that can adjust the frequency of the 12V AC as well as the amplitude of this signal. If for example, you only control the frequency without controlling the amplitude, you'll change the designed motor-torque characteristics of the pump, ie, the change of the speed of the motor isn't linear to the change in frequency. Probably make the motor fail prematurely.
For me, if I want to control these pumps, I'd get a DC adaptor rated somewhere at 15V 5A (laptop adapter works too). Put the DC through a DC-AC inverter driven by a PWM signal to adjust the frequency and amplitude AC output. There's alot of details you need to look at to make it work w/o risk of damage or overheating."