If we don't use any gas heating, we're at 79ºF in the morning and 83ºF in the afternoon using solar and a dark opaque electric safety cover (not as insulating as a bubble-type cover). Without solar, the water would be more like 50ºF to 55ºF so we're getting a roughly 25ºF to 30ºF rise this time of year which is pretty good. If we had a clear bubble-type cover with no solar panels, however, we'd get a reasonable gain, but probably not much more than 20ºF and we'd be losing chlorine every day from the UV in sunlight.
Is there anyone in the San Francisco Bay Area getting their water above 70ºF to 75ºF with a solar cover alone (no solar panels) this time of year?