For those of you who live in cooler climates, I thought it might be worth sharing the following tips for helping to keep your water nice and warm, and save money on heating (if you have a heater).
1. Shut off the pump overnight, or whenever it's cool out. Run your pump during the warmest part of the day. I think this is especially important when you have a gas heater like I do, because my guess is that the design of the heater -- maximizing heat transfer from flame to water -- makes it act like a heat sink when the outside air is cool and the heater's off. My guess is an electric heater would be similar. But even if you don't have a heater, the movement of water through your plumbing, and the circulation in the pool will expose more warm water to cool temperatures, robbing the pool's heat.
(Note a lot of people in Winnipeg keep their pumps running 24/7 because electricity rates are pretty cheap here. The previous owners in fact told me to leave it on 27/7 because "it'll go green pretty fast if you don't". But they obviously weren't using the trouble-free pool care methods.)
2. If you need to add water to the pool, and you have a heater, add the water when you would be running the heater anyway, and put the hose into the skimmer. This will make your heater more efficient because it's heating up cold water. (note if you're trying to heat the pool as fast as possible, then obviously you wouldn't do this - wait till later to add the water then)
3. As a corollary to #2, consider adding water to the pool in small doses. We have a dark grey hose that gets really hot in the sun, with a shut-off attachment at the end of it. When we're hanging out in or near the pool we just run the hose every ten minutes or so, for about 20 seconds until the water comes out cold. (It's often so hot it could almost burn you!) This tends replace any "splash out" water so by doing this I haven't had to add any cold water the pool at all!
4. When putting your solar cover on, try to minimize the amount of water that gets on top, because some of this will probably evaporate (causing some heat loss). I've found that leaving a little fold on the front edge as you unroll it, and having someone help unroll the cover so you can keep the front edge above the water, really helps.
Those are just some of the tips I've happened upon. Of course there are also the obvious ones that have been covered in other threads, like just generally using your solar cover appropriately (hint: it really protects against evaporation so very useful on dry or windy days even when the outside temp is high).
Does anyone have any other neat tips?