MY FISH ARE DIEING?!

Question
Four months ago I got two fantails, both young and energetic. Suddenly yesterday I return to find one floating on its side at the top of the water not moving much, hardly breathing. I quickly isolate this fish in fear of disease and in the morning find it dead:(
After checking on my final fantail I also discover it on its side hardly moving at all or breathing. I have put the fish in shallow water with a bit of salt. What is happening and how do I cure it?  

Answer
Hey Jon,

Check the fish over for abnormal swelling, discoloration, fuzzy material, or any other signs of disease. If you cant find anything, then let me know. Get a water test, and gather up all the details you can, and we'll settle the problems you've having.

Sorry i couldn't be more of an immediate help, try thawing out peas and cutting them up as food. If your fish wont eat, odds are, it wont recover. Sick fish who stop eating, things don't look good.