Getting your pool to warm up depends on two factors: How much heat can your pool absorb each day and how much heat is it losing each day. The net gain is the rise we see.
Every day in the summer expect your pool to absorb a lot of heat just from sun exposure. The problem with passive heating (or active solar via solar panels) is they’re really only effective to the net gain IF we can stop all that heat from escaping at night. Solar covers are the cheapest way to reduce evaporative cooling at night or on a windy day. I don’t find they make the pool heat up faster during the day, but if it’s windy they definitely contribute more to keeping heat loss down.
The other more effective options are a natural gas or propane heater. These heaters produce several hundred thousand BTUs of heat in the pool. The downside is the cost of equipment, installation and gas.
Electric heat pump heaters are another option which I know a small amount about.
I have a diy solar setup that gives about 15-20% more heat each day than with no heater at all. It’s maybe 1-2 degrees extra daily. All day gains are lost at night if I don’t cover the pool, even still I expect a 5-6 degree drop minimum for a typical summer night here.
All that said weather is my biggest helper for keeping water warm! More sun means more fun!
The heater was a little over $1k on sale, its a Pentair 125k. I had an HVAC guy connect the gas, that was $150. Mine is located only about 5 feet from the actual meter and they used 3/4 line. I believe my model allows for 3/4 under 50 feet, the farther from the meter the bigger the line, specs for each heater are pretty easy to find. I haven't gotten a gas bill yet, I know there are some apps that will read your meter but I haven't tried them. I saving so much money with my daughter not playing travel soccer this spring I haven't thought about the cost to run it yet.