HI everyone! I’ve had my goldfish tank set up for about a year now and just recently noticed that there is a stream of bubbles coming up from under the substrate. I have a bubble bar in the back of the tank but these bubbles are coming from a separate spot. The tank also smells vaguely like sulfur.... I am curious whether this is an air pocket, and if so, what should be done about it. It’s tempting to stir up the substrate where the bubbles are coming from, but I wasn’t sure whether that could be a bad idea.