TROPICAL FISH LIQUID SOLAR BLANKETLiquid Heat - Solar Pool Cover in a Bottle - Reduce Evaporation, Conserve Heat - 310mL-(Pack of 3)

Q: how long does it last?

We add it every 30 days as per thr instructions & it works great. Will never go back to a solar cover.

Q: Does it warm a cold pool?

This does not instantly warm the pool. I use it as directed and what I notice is a very hard to see thin layer on top of the water that absorbs the sun's warmth. You can only see it at an angle in the sun. What the product does for my pool is warms it by about 5 degrees. I live in Pennsylvania so this extends our swim time into September. My Aunt now uses it and she could see the difference. Check your thermometer before you apply the product. You will see a difference in a couple of days .