Two things:
1) This is my view right now.
2) I just had an ephiphany! I remember reading that during the ich life cycle, it drops off the fish, typically at night, and then encysts into the tomont stage. After 3+ days, new ich theronts will release and find their next host. What makes ich so devious is that it literally falls off where the fish sleeps, and then when it multiplies and releases again, it'll release right where the fish is sleeping and reinfect the host again and again!
My epiphany is the fact that I turn down my water flow at night. The stillness of the water is the ultimate environment for successful reinfection! The ich theronts don't have to fight flow and can lazily swim right to their next host when they release at night!
In a perfect world, I should be ich free by March 3, that's 76 days of running the tank fallow. But just to cover my bases, I'm going to reprogram my flow to be just as active at night. That, combined with my oversized UV, should help a lot if ich finds its way back into my system.
The flow issue makes more sense now as I think about the powder blue tang that lived in the sump for 3 months without showing any signs of ich at all. The sump had tons of good flow through it. Even if a theront managed its way into the sump to get to the powder blue, the water current in there was much too fast for it to latch on, even when the fish was more still and sleeping. Even if a tomont cyst happened to form in the sump by the sleeping powder blue, once all the ich theronts are released, the flow would just push them all away making it more difficult to attach to the host.
Hmmmm.... Interesting... Just a theory of course but it does make you think.