I have an established tank of 10 years. No new fish in quite awhile. I have a pair of clowns over 10 years old. One became pale and quit eating last week. A few days later he began swimming back and forth non stop at the top of the aquarium and breathing rapidly. He’s since settled back down. However he’s still not eating and breathing fast. I really just thought it might be his time as he’s quite old but now it’s been over a week and he’s still hanging in there so now I’m wondering if there is something wrong that is treatable.