I'm sorry, I haven't tested other thermistors yet.
If the DC resistance of the 24V air pump is less than about 7 ohms then you should use either a surge-suppression thermistor (or other surge reduction device) in series with it, or an external mosfet switch that can handle the surge current. You could try a 7 ohm resistor in series, but that may get rather hot and also limit the pump speed.