Is the pool itself in the sun?
Solarcovers.com has nice clear vs blue solar covers...
They also have interesting $0 60" diameter "sun rings" with 6 magnets
to keep them in a hexagonal kissing pattern (one circle surrounded by 6)
and make them stick and slide together so they can be removed by a person
standing in one position. They recommend 12 for a 24' round pool, which
would leave 48% of the water exposed.
You might make your own 6'x5.19'-tall sun rhomboids with 31 ft^2 of solar
cover and a bent PVC pipe and a 60 degree elbow and 4 magnets... 12 would
cover 83% of a 24' pool in a tight hex pattern, except for the perimeter,
which could have a 2'x12' greenhouse polyethylene film skirt attached to
the pool wall.
Or make a 24' greenhouse polyethylene film pillow with a perimeter PVC
pipe ring and a small tube running across the diameter inside and a float
with an opening at the top of the tube in the center. Deflate the pillow
so it sinks to the bottom for swimming, and reinflate it to float it.
With a dark bottom, 1080 Btu/ft^2 of unshaded sun might keep the pool
34.3+0.9x1080/24h = 74.8 on an average 34.3 March day and 51.1+0.9x840/24
= 82.6 in October. For more sun, you might add a reflective half-cylinder
above the north wall of the pool. For more insulation, you might inflate
the pillow with soap bubble foam at night.