Ouch, shocked !!

[spreerider]

you can get voltage in the water without a actual leak, the AC current in the motors can induce a voltage in metal equipment that is within the electric field surrounding the motor. i would check to see if the pumps are close to a motor or if your ballast is close to metal in the tank.
the reason an arc fault trips on a MH is that the MH is an arc in the tube, some larger CF's can also trip arc faults, this can be a problem if you want to use energy efficient bulbs in your bedroom.

[Doug]

Originally Posted by spreerider

you can get voltage in the water without a actual leak, the AC current in the motors can induce a voltage in metal equipment that is within the electric field surrounding the motor. i would check to see if the pumps are close to a motor or if your ballast is close to metal in the tank.

Understand what you're saying but dont follow the last part. What type of motor would the pumps be close to, exept their own. My ballast is in the stand, under the tank.

Perhaps the voltage measure from the Tunze, is created as you say but it also wont run on a GFI.

Thanks