“...the pool is easier to clean, uses less chemicals, and the magnesium salts do not need to be replenished often, as there is no rain diluting the water.”
You are absolutely correct that the enclosure has made our pool at least 200% more useable than it would have been without, probably more like 500% more useable. Both for the fact of the warm room when even a little sun shines, and the absence of wind.
Also, the pool is easier to clean, uses less chemicals, and the magnesium salts do not need to be replenished often, as there is no rain diluting the water. The enclosure itself acts as a very good solar heater. In addition we have a thermal blanket which pulls out of the cover pit at the deep-end, which we use nearly every night, except when it is almost too warm to swim (over 32 sometimes.) Once the night temp starts dropping, the blanket helps overnight, and the cover adds to the benefit, so we lose only 1 or 2 degrees overnight, which, with our winter sun, stabilized last winter at 18 degrees. For me, that was still swimmable. Yesterday 26, today, with wind and rain again, probably 25. And no leaves blowing in, only a little clay from the bank we cut to make a place for the pool.
Client - South Island