I'm new to planted tanks. I have a planted 5 gallon with Green Cabomba. The tank has one fish and is in the process of cycling. I just did a 50% water change. When I topped off with clean water, one of the Cabombas had a stream of air bubbles coming out of the top. See below. At first it was a steady stream but it has since slowed way down. What is this? Thanks!