Bests & Worsts Reviews from Amazon

We purchased this and all parts *appeared* fine. It was relatively straightforward to set up and if took 3 days to heat from 52 degrees to 104. We set it on an otherwise empty concrete patio, on top of a rubber/foam puzzle mat for insulation. We plugged it into a GFCI outlet and made sure at setup and each time before use to test/reset. It should have worked fine. We were able to use the tub several times and it was lovely, *however* on several occasions, after exiting the tub and while covering it, I received a zap/electric shock to my finger. Very confusing as we had just used it. The last time I went to use it, though, after I uncovered it and before I got in, I touched the surface of the water and got shocked. Called my husband who came out and he felt nothing. I said take off your shoes which he did and then he was shocked as well. There is NO other indication of a problem- no apparent visible defect, no error message and like I said, the test/reset at the outlet worked fine. Extremely alarmed by this, we had to dismantle the tub and ditch it. We are being issued a full refund. Customer support of the merchant, likely sharing our concern, refunded us, but I wish I also understood what the problem is. What a shame, but of course I'm happier to stay safe and be alive!