We raise the temp to speed the ich life cycle, salt at 3parts per thousand and above kills the ich in its vulnerable stage.
The paragraph below is from an article called Tilapia toxic.
There are three stages in the life cycle of ich. These are the adult stage or trophont, a cyst stage where asexual multiplication of the parasite occurs and the tomite stage which is the infective form of the parasite. The trophont stage is embedded in the skin of the host fish. The trophont stage causes damage to the fish, the extent of which is related to the number of trophonts present (e.g. the more present, the more damage is done). In particular, the abundance of these parasites on the gills causes the greatest threat to survival of the host. Trophonts are covered with short cilia and while on the host move between the layers of the skin and feed on cells of this tissue. These trophonts increase in size and can be recognized as the þwhite spotsþ that are characteristic for fish heavily infected by ich. Once mature, trophonts drop off of the fish; fall to the bottom of the container as a cyst stage and multiple to form 500 to 1000 tiny, motile tomites, the infective stage of the parasite. After three days the cysts rupture releasing the tomites. Tomites must contact a host fish within three days or the organisms will perish. When a tomite makes contact with a fish, it burrows into the skin and grows to form the adult or trophont stage.