Before anything else, you might want to (a) learn more about the stages of c. irritans, (b) ambiant temperature-calibrate your refractometer, (c) DO NOT USE COPPER, (d) re-do your hypo, and (e) see if you can donate your inverts to the LFS
Garlic doesn't treat ich. It's not even considered a part of a treatment. It is fallacy to assume that the blood-sucking ich are vampires who will die at the presence of garlic. There are no empirical scientific evidence that the parasite is affected by garlic.
Garlic may help boost the immune system of the host fish; thereby making the host resilliant to other secondary health problems caused by ich. But that will do nothing to the water itself.
Copper is a dangerous remedy to deal with because it is not easy to remove traces of copper in a tank. In case later on you start to gain interest in anemone, corals, and such Copper is a bad idea.
There are stages of c. irritans that can react to certain treatments and won't react to others.
I had a bad case of c.irritans that made me hypo the display (not encouraged to others, of course). I lost snails and a few fish. But my target specimen (Blue Hippo Tang) survived with flying colors.
Raising the temp only helps to speed up the cycle of c. irritans. This is effective in making the c. irritans fall off of the fish quicker. But it's still all over the tank.
Starving them of host is a good plan of yours which may take at least two months.
Hypo will work if it is done right. It took me from Sept 2005 to Jan 2006 for the treatment.
Remember, even after a month that you don't see symptoms on the fish anymore, it doesn't mean you erradicated the c. irritans. Be patient. That is the key.
It's a five part "bible" on treatment. If you have the patience to read this, you can have the patience to actually perform hyposalinity accurately and effectively.
In terms of inverts not hosting (snails especially), hosting means that the c. irritans is able to bury itself into the host, feed off of the host, and lay eggs. It may not host snails, but it may be there stagnant on the invert. It is scientifically possible.
So good luck and I do hope you can erradicate c. irritans from your hobby. Once that happens, you won't have problems for a looong time with c. irritans. Ofcourse, QT-ing is the key. For LRs, recure them in your house for 6 weeks. This will also help make sure there are no c. irritans sitting on the crevices.