Hey there,
For my pool i was looking at an electronic solution till i finally decided that salt water and electrics dont play nice.
I eventually got a 150 dia PVC, glued an end cap on one end, cut it 600 long and glued a screw on cap on the other end. I then put a toilet cistern fill valve inside with a 40mm connection to my pool and then just set it to stop at the right height, drilled an overflow above that height and plumbed that away for when it rains and my pool over fills... job done and has been maitenance free and worry free for 2 years now.
I can take a few photos of my setup if you think its something that you would be interested in looking at?