Ok, from what I've been studying on Ich...
Ich is a parasite that is in every body of water.
The reason ich effects our fish negatively is
A) large colonies of the parasite
B) weak immune systems of the fish
I have read countless articles saying that if the ich is not effecting the fish to the point that it's not eating,, garlic and vitamins can help boost the immune system to fight off the parasite.
Saying garlic "has no effect" is kind of misleading. Garlic has outstanding antimicrobial properties, and introducing it to their diet will help fight off a large amount of the infection.
A multivitamin in addition to garlic can help give the fish the nutrients it needs to build it's immune sytem, and fight off the parasite.
Ich is in every single body of water on the planet, so by removing the infected fish, you aren't really addressing the underlying cause. Especially if there are other fish in the tank, this becomes simply unrealistic, as every other fish is being exposed to the same thing the infected one is. So in turn, it's an issue with the infected fish's immune system.
You need to do several water changes, feed the fish garlic alongside a multivitamin.
If it does not get better within a week or two, no amount of QT will help because it's immune system has fallen far beyond what can be repaired, and the parasite has already taken over its host.