HELP! My telescope fish is dying!?

I have had my cute little telescope fish for over a month now. I was watching him swim around normally about an hour ago, and I checked on him right now and he is losing balance! I changed his water and now he is still not looking too well. I even put some salt in the water ( Is this true??) which might help his natural slime coat. Please help ! I love him so much and it hurts to see him suffer like this. IS THERE ANYTHING I CAN DO?