Simple Solution. Works 99% of the time...
Turn temp up to ~84 Degrees. At this temperature Ich's free-born (water) cycle is about 10-15 hours at the maximum. It has to find a host within those first 8-12 hours otherwise the cell that causes Ich doesn't have enough energy to be successful.
If you have co2 turn it down some. Otherwise leave the rest of the tank the same and possibly add a very LIGHT amount of epsom salts. 1 tsp per 20 gallons. Most of the time you can get by without the epsoms.
Also if your medicating the tank, TAKE OUT CARBON BAGS or any thing besides bio media (ceramic balls, mechanical fibers). Carbon will remove the medication as soon as it touches it.