Hello. I noticed that my diamond goby was swimming at the surface and putting his mouth out of the water (like he was trying to eat food off the surface) and i wanted to know if something was wrong or if this is normal. There is about a 2 inch gap in the back of my tank that isn’t covered so my water evaporates fast and the water line is low right now so my filter is creating bubbles. could he be trying to eat the bubbles? i’m just looking for some answers. thank you