Shrinking air (gas) hole

Of course the purpose of the air is two fold. Utmost, it allows bad gases that accumulate on the bottom of the pond (where your fish are sitting all winter)to rise and escape out of the pond and help replace much needed O2 in your dormant water. Water changes even during the winter are still recommended. I look for those warm days and drop a sump pump down that hole. We run a hose I've kept in the basement from the kitchen sink out there to refill. If you were a fish, would you want to live in the same water for 5 months? In our part of the country, water changes help restore Kh levels which help to stabilize the Ph. Even though we've quit feeding and the fish are at rest they are still breathing down there and while the colder water helps to convert the ammonia to lesser dangerous ammonium, as the water warms up it will convert back, so water changes still help maintain good water quality. Living in near freezing water for 4 months is stress enough, lets help them out by keeping their water fresh.