I try to keep mine as full as possible (top of skimmer) - because we live in the country and water is costly, so rain is always welcome to top up the pool since dry spells can last a long time, that extra 3" is very welcome! Then, when we use it, it gets splashed out and evaporates and of course, you always lose some to backwashing - which I try to do right before rain is supposed to come. Leaving the solar blanket on keeps dirt out and evaporation to near nil. It's never bothered me that the skimming action is affected because it's rare that it collects floating debris on top (due to being covered) and when it does get some Crud floating on top, out comes the leaf net and in 5 minutes it's all gone.