Several inexpensive upgrades that most any pool and especially a solar heated pool can benefit from are:
Replacement of inline chlorinators with similar offline designs.
Upgrade filter interconnect piping to all 2 inches and replace ‘hard’ 90 elbows with ‘soft’ 2 in sweep elbow designs.
Incorporate 2 in full flow ball valve, multiport valve and check valve designs and eliminate unnecessary bends.
Install an optimized energy efficient single-speed pump, increasing flow while reducing electric use 50% or more.
Employ an inexpensive solar blanket (without the elaborate and unsightly reel systems) during spring and fall on cooler nights (below 65) to prevent potentially unrecoverable heat loss. This can be one piece or cut in half or thirds for odd-shaped pools. Of utmost importance is to cut the cover undersized so it lays directly on the surface of the pool with no air space or overlap.