I bought a 3" silver aro about a month ago, feed him pellets once or twice a day depending on my work schedule, and change 25% of his water every other day, maybe every third day if I'm lazy or tired, but he acts strange every time I change the water. It looks like he's sneezing: he opens and closes his mouth really fast time after time. The water out of the tap is a bit colder than the tank water causing a slow temp drop from 82°F to 79°F. He's still alive and thriving obviously since he never has trouble eating, swims next to my hand when I put it in the tank, and has literally doubled in size from the time I bought him, but I'm just curious to know what he's doing and has anyone ever heard of our seen this before.