I would suggest continuing the salt treatment, increasing the temp to 84 should be sufficient, as the ick parasite cannot survive long at over 82 degrees.
Just for clarification, ick ("ichthyophthirius") is a parasite, not a viral infection. It is caused by the cilliate "ichthyophthirius multifiliis", an organism, pear-shaped to spherical in shape and .2 - 1 mm in size. (the macronucleus is horse-shoe shaped and the micronucleus is spherical). Ick spends most of its life on a host fish, feeding off the skin, digging sealed off hollows into the flesh. The parasite has a 3 stage life cycle: 1, growth, spent on the skin, 2, cyst, when it drops to the bottom of the tank protected by a gelatin covering and then dividing, and 3, the infectious stage, when pear-shaped zoospores seek a new host. The cycst can divide into as many as 1000 zoospores, which have 70 hrs to find a new host. Ick is highly contageous, and survivors can acquire an immunity, but many remain dangerous, since they may be carriers without showing signs of the disease. This is why medication is the #1 solution to resolving the issue.
Because of the temperature tolerance limit for the parasite, using the salt treatment of 1 tbsp/5 gallons and raising the temp to 84 degrees should safely rid your tank from the parasite. The salt will effect the parasite also, and will act as a muscle relaxer for the fish. The use of salt can also help to avoid/prevent the chances of secondary infection in the fish.
Sorry it took so long for me to respond, I was having a problem logging in over the past couple of days. I hope this helps.