You really shouldnt buy things without checking what the fault is.
Fault diagosis 101 dictates you should check each component in a logical order.
The first an obvious thing to do would be check the battery and the pump, so grab the pump that is running slow and put it direct to the battery, if its better it was something between the pump and battery, (connection,controller etc) if its the same its either the pump or battery at fault.
so grab another pump thats known to be working fine and put it direct to the battery... if that the pump is the same its likely the battery, if the other pump is better then its the pump.
If its neither the pump or the battery i would remove the controller from the equation, if all is good probably the controller if all is not good then you need to look somewhere else, air lock, kinked hose, electrical connections.
you get the idea anyway, last thing you want ti do is phone up brodex and say "whats wrong" because they have no idea and just want to sell you something.