Funny smell in my aquarium?

Today my tank had a smell to it. I tested my water and I had the same results. The smell is why I tested. I would just keep an eye on it. That's what I plan on doing with my tank. I would only change out 20% of your water at a time. My tank is 3 months old today. That my have something to do with it. I change out 20% of my water every week.