I see your reasoning, but why would you expose a fish that doesn't have ich with water that has it? Seems counterproductive, although I see what you're trying to accomplish.
Gotcha!
But if the Achilles was treated for ich completely in qt, and your DT was not ( I am assuming wasnt) how did the Achilles fare when you introduced it back into an infected DT? Or did I miss that the DT was fallow after exposing the Achilles and before introduction into the DT?
My DT has over 40 fish and it hasn't gone fallow and still has ICH in it. Even though all of my fish are doing great, and I haven't seen the the Hippos with any spots in months, but there is still ICH in the tank. That is why I transferred water from my DT to the QT system, this way the Achilles could have the same water as the DT with ICH. If the Achilles would have broke out with ICH because of the water coming into the QT from the DT, I could have treated him in QT.
By the time I transferred the Achilles into the DT it was living in the same water from the DT and he was healthy and without ICH.
If there is any fish that will catch ICH, its the Achilles. However, a very healthy and stress free Achilles has a much better chance of not catching ICH than a newly acquired Achilles that hasn't gone through QT and dropped directly into a DT.
I have a good friend who has had an Achilles in a 180 Gallon QT tank for almost two years (of which is now the Achilles tank). Every time he tried to bring water from his 900 Gallon DT into the Achilles QT, his super fat and very healthy Achilles was covered in ICH within a few days. Even though not one fish in his 900 Gallon reef has shown any signs of ICH, the Achilles came down with it in a few days. We have discussed this and believe that their are different levels or strains of ICH, some stronger than others. Over the last two years he has done this twice and the same results both times. He immediately treated the QT tank with Cholorquine Phosphate and within a few days the Achilles was back to normal again.
Before I purchased my Achilles, he was going to give me his because there was no way for him get it into the DT and live. Plus in a 900 Gallon, good luck trying to catch him.
He had him ready to bring to my house and decided against it, because of a few very valid reasons. 1. The Achilles was doing great and super healthy in his 180 Gallon and he would hate to see it come into my DT, get ICH and possible die. 2. He would feel horrible if I put the Achilles in my DT tank and the outbreak could possible create a chain reaction and wipe out all of my fish. 3. Every time he went into the fish room, the Achilles had become this amazing pet that would greet him and get all excited to see him.
After the great results I have had, He may try it one more time with the hope the his Achilles may have built up some type of resistance to the strain of ICH in his DT tank. Time will tell, and maybe he will be in this chat with an Achilles success story.