LED check circuit on startup
If you use arduino why dont you do this start-up test in code? If you have still reason here can be some inspiration. After powering this circuit the Led starts to glow immediatelly, then after C1 charges to 4.3v the transistor become off aswell as Led. You can connect the Led to your fluid controll circuit according your needs.
Change R1 according your led wattage and power supply voltage.
Green is current thru Led, blue is the Cap voltage:


Edit:
For fast discharging the Cap to repeat cycle you can add a reverse connected diode D2 to discharge Cap thru R4 once the power supply is disconnected.


Edit:
Maybe more suitable would be an NPN version of this circuit. It is possible control Led with whatever voltage in range 2-12v. (0v the Led is off).