The blue tarp is actually heavy duty bubble wrap and is the proper size for the pool, it lets the sun through to warm the water and the bubbles help insulate the pool at night and stops the evaporation which is the biggest heat loss from the pool. I'll get one of those wind on reels for it as it is a pain to put on and take off even with two of us, with the 5.5m round pool we had before, it was easy to take on and off and it really makes a difference, at night the pool can cool off by about 8c without the cover and with the cover on it only goes down by about 1c to 2c depending on air temp.

the pool is rusty, and it happens every time I use ground water to fill the pool or hot tub, I have used tap water and that did not go green or brown but it's too expensive to waste drinking water like that.