What is the purpose of a variable pump. I'm trying to understand my new build better. While dealing with some deck drain issues with the builder. I have questions about how it works with my cleaner mode pool mode on n running my water feature without putting the strain on my skimmer. Noticed one day with vacuum out n running at cleaner speed.Skimmer ran low an let air in at times. And I filled pool with more water more than recommended. Thanks for all n any input.