Adding salt will cause a fluxuation in the waters salinity that will kill any free swimming offspring - it will also burn the slim coating of the fish removing some off the adults. Increasing the Temp speeds up the metabolizim of ick thus shortening it's lifespan. The key to prevention is low stress levels, clean water, plenty of dissolved oxygen, and a healthy varied diet. A fish with a healthy immune system usually will not suffer from Ick.