I stopped covering my IG several years ago for various reasons. I do keep a couple 5 gallon bucket holes so I can access liquid water through the ice. I think the record is 17". Like Watermom, I like to play and try and get a jump on Spring. I do raise the pH and hit the chlorine as late as possible and generally have no problem in the Spring. I have never added anything while closed. While my regular equipment is winterized I can use an old pump and PVC pipes into those access holes to jury rig circulation if I ever had to.
Al