Fish swimming near the surface and gulping/eating as if there is food.?

It looks like the water in your tank is de-oxygenated. Do you have airstones working in your tank? They help aerate the water significantly. Also is your water cloudy? That could be sign of a bacterial bloom. I once had a yeast co2 generator that was working in my planted tank until one day the water backed up from the generator into the tank which the yeast from the water consumed most the oxygen in my aquarium. Luckily I was able to spot this in time when I saw the fish starting to gasp for air and the water was cloudy. I changed the water and installed in multiple airstones in order to help aerate the water.