Hello, another newbie here. Anyways, I just bought a used Cal Spa from a guy here in town. I wired it by running a dedicated 240V circuit from my main panel to a sub panel. The sub panel has a 50 Amp GFCI disconnect. The equipment pack in the hot tub has its own GFCI as well. It worked great for about 14 hours. It came up to temp and was working properly, turned off properly and came back on when it needed to. After a while, the GFCI on the sub panel tripped. I turned everything off, switched the GFCI back on and the hot tub started up (with the themostat in the "off" position) I called the hot tub guy and he came out to take a look at it. Immediately he was like "You can't have two GFCI operating like this. There should only be one." He wants me to either disconnect the equipment pack GFCI or the sub panel GFCI. I don't think that sounds safe. Is it common to have 2 GFCI's like this or, should I have just one?

Aha the old "you can't have 2 GFCI" urban legend theory. Think about this, now bathrooms have to have GFCI protected outlets, and hair dryers too have GFCI's on their cords, the combination works every morning for millions of people. You can have 2 GFCI's on a circuit, they don't interfere with each other, it a myth.

No as for your problem, GFCI troubleshooting can be tricky, first you have to establish wether it is tripping on high amperage, or tripping on ground fault. Get an AMP meter to verify AMP draw, check wire connections to make sure they are tight and secure, if you have a loose connection it will generate heat which in time will trip a breaker. Try disconnecting the heater element and run it for a day cycle if on and off. It could be an element is getting ready to totally fail, perhaps it has a pinhole in it and as it heats up and expands you then get a ground fault.

Good luck.