Some types of centrifugal air blower or water pump require a minimum air or water resistance connected to the outlet of the blower or pump.
If connected to an open ended outlet they draw more current, possibly enough more to overload the motor.
This is counter intuitive, one might expect an obstructed outlet to increase the current drawn, but this is not the case, and may be confirmed by experiment if desired.
If the air blower in question is intended for aerating water, this implies that it is intended to generate appreciable pressure, probably to force the air through small holes in a submerged pipe.
If the blower is run connected to an open ended hose or pipe, then the air resistance may be insufficient and the motor overloaded.
I would suggest a BRIEF trial with an open ended pipe and noting the current drawn.
Then connect up as intended and again note the current.
You will probably find that with the open ended air discharge that the motor current is excessive.
A motor overload trip seems desireable, either the tradditional thermal relay or a more modern device giving similar protection.