Quick Update, after a long silence.
First - Picture from Saturday, as the FC drifted below 10, on its way to 6. (I love how you can see the shape of the deep end from the 2nd story window cell phone picture!)
(The wind unrolled the solar cover a bit, and it dipped back into the water, I wasn't keeping it like that on purpose.)
I took a plunge on Saturday into the balmy 68 degree water to retrieve the quarter, which I confirmed was actually tails, and not my terrible eyes playing tricks on me.
On Sunday, I got back in at 70 degrees, and my wife and son joined me for a bit, near the end. (Wife didn't want to go past her knees, with the temperature where it was, but my 2yo son loved every jaw chattering minute of it!) Rain in the forecast for most of this week, but hopefully the water warms up more by the weekend, and we can enjoy it a bit more.
Definitely considering installing some solar heaters (tubes or mats) either later this summer or early next spring when I open back up. I just need to do my homework and price-shop the various solutions out there first.