I live in Michigan and have a Radiant metric GT pool which is installed completely inground. My plan for closing it was to use a skimmer cover and not drop the water level at all, but I have not been able to find a cover that fits. According to Radiant I should drop the water level, just below the skimmer. I don't want to drop it too low, how low should just below, the skimmer be. I will be using a mesh cover on the pool so rain and snow will get in. I'm worried if I drop it too low, it will affect the strucural integrity, but if i leave it too high it may hurt the skimmer. I will also be using a gizmo.

Unless you have very high ground water levels you should be able to drop the water level up to 18" without any problems. Of course there isn't usually any reason to drop it that low, I'm just saying you have some room to play with when lowering the water level.

With a mesh cover you want to drop it about the same amount that you expect to get rain/snow over the winter. How far that is varies from place to place. Many places about 6" is plenty, but that varies. If you are worried about it, it is often possible to setup a cover/sump pump on a step so it keeps the water level from getting back up to the skimmer.