1) stop adding anymore fish
2) with no fish in the tank, do a 100% water change
3) raise temp to 87F
4) add 3 tablespoon of aquarium salt per gallon of water
5) add some pure ammonia from walmart until your test shows a reading of 2ppm
6) maintain an amonia reading of 2ppm, temp 87F, and the initial 3tablespoon per gallon salt level for the next 4 weeks
7) after 4 weeks, reduce temp to 75F, bring salt level back to 0 through water changes
8) order some fish online (aquabid, petsolutions etc), your LFS are obviously selling you diseased/sick fish.