I believe strut is also available in aluminum .... check McMaster-Carr for a full selection.
OK, fine, use PVC .... but support it as continuously as you can. Like, lengthwise along strut as pictured with the clamps I linked to. You could even do most of that using wood and 2-hole straps.
The key is complete support under the PVC for the entire length. Otherwise, PVC will sag, look poor, and it becomes brittle with time. There's also the risk of the pipe being used as a tie-off point foothold, etc. These are additional reasons for 'going big.'
As for the fear of electrical shocks in the water .... just a silly idea here ... How about running a #4 copper wire down each pier into the water, and bonding them to your circuit ground? That would surely reduce the chance of any "voltage gradients."
Contrary to common practice in our trade, I'd also clean & prime the PVC before applying glue.
BTW, stainless conduit and fittings exist.
Last edited by renosteinke; 06/08/16 11:39 PM.