Hospital tank set up advice, please comment on plan

[Delphinus]

Ugh. Thanks for the all the replies. I have to say it makes my head swim though. So one the one hand butterflies are sensitive to hyposalinity. On the other hand butterflies are sensitive to Cupramine. Aaaaaaaa!

What's completely bewildering to me is that I had them for over 18 months, ich-free, in a tank where one of the tangs had occasional spots on and off for 18 months, but never more than a half-dozen individual white spots, so was never a huge concern to me. Now that fish is in another tank and completely ich-free, and these guys have a nice large tank to themselves so you'd think they'd have less stress, but when the spots come back they are really bad.

Is 20g big enough for 2 butterflies? When I hear stuff like 90g QT/hospital tanks I start to wonder that treating two butterflies in a 20g is a recipe for more trouble since clearly they just stress out over little things.

The tank is not a full blown reef. In fact, there is nothing in there except the 3 fish (2 butterflies and a tiny eel, who completely ignore each other), live rock, the occasional snail. Would there be any benefit in rehoming the eel into his new tank and then simply lowering the SG in this tank to something like 1.019-1.021? Recognizing that this will not kill the ich, but, 1) it seems to me nothing kills ich anyhow, it's always there, just not able to infest fish when they are healthy; and 2) this way they are in their home, comfortable, still eating, etc. Then I shore up the UV and maybe garlic the food, or add vitamins or whatever .. and see what happens?

My hesitation is that I did try hypo on some pyramid butterflies a couple years back when I bought them and they developed ich. That episode was a complete failure. If they're just going to die anyhow then is it kinder to let them die in their home as opposed to speeding it up in a doomed attempt at treatment in a 20g ???