I can probably help you out on this, but I'll need more info . . . .
Can you give me more info on the output of the aquaero, . . .
15khz sounds like a PWM base frequency, that would change duty cycle to effect control.
How big of a resistor did you try with it?
What is the output supposed to output to?
All the info you can give me will help.
I guess you don't have a scope, do you?
Knowing the P-P voltage and if it's a square wave, (as I expect) would indicate if it's a power source, or only a control signal for a driver PCB.