How to eliminate stress in my aquarium fish?

I got a 10 gallon tropical aquarium tank with 1 flag tetra, 2 fancy guppies, 2 hybrid tetras, 2 zebra danios, some kind of orange fish (is compatible with others), and recently added a golden algae eater to clean the tank. I understand the rule of 1 gallon of water per 1" or mature tropical fish and I have roughly 11 inches of adult fish in total. All the fish are doing well and eating except the orange fish who appears stressed out and just hides beneath some rocks I put in the tank. He comes out occasionally to eat and does not move around like he used to. His scales are rugged looking, so I added some salt to try to restore the condition of the slime coating, but I don't think it worked, I perform weekly water changes of 10% or more of dechlorinated water. My pH is a little on the high side, but that is typical with Tennessee tap water. Does anyone have any suggestions on how to bring this little fish back to himself and have my aquarium thrive again?