I don't see anyone not being civil on this thread. (Unless of course you count your outburst at people trying to share knowledge).
Ok, you're not a newb and you're not a child but you are definitely being stubborn about this. There is not a single reputable scientist who will back you up on your garlic treatment.
Here is how ich works roughly:
1) It is attached to the fish. It feeds off the fish to gain strength.
2) It detaches from the fish and settles on the sand/rocks. At this point it starts getting ready to reproduce by forming cysts. This is why you think that your fish gets better because the ich has detached and is getting ready to multiply.
3) The cysts burst and release thousands if not millions of free floating parasites that swim around looking for a fish to latch onto. In the ocean this isn't a big deal because the ocean is huge. In an aquarium's confined spaces, they will easily find ALL of your fish.
4) They attach to the fish in greater numbers than before and start the cycle anew.
This is why it seems like the fish gets better and then suddenly gets hit by a worse case of it. The only way to clear your tank of ich is to remove all your fish so that stage 3 is disrupted. The little swimming parasites will swim around looking for fish and when they don't find any, they die.
In the meantime, you put your fish in an environment that will kill any parasites still attached to them. Copper and Hyposalinity will both do the trick in killing the ich but this will also kill your live rock, live sand, inverts and corals which is why it must be done separately.
Anyways, I'm done with this thread. I don't want to argue with you. I'm just hoping you'll absorb and apply this knowledge and maybe something can be done to save that tang and any other fish you decide to put in your tank, because I guarantee that until you leave your tank fishless for 6 weeks, they will all catch it as well.
