Oto Dying and Copper Question

[garfieldnfish]

I have bought 2 zebra otos 2 weeks ago. About 3 1/2 days ago one of them was affected by the typical oto thing that all of mine seem to die from. I have had one female resident oto for 2 years now, but every other oto I have ever added to her tank has died within less then three months. I believe her to be a carrier of some disease unique to otos. I had given up on otos until I saw the zebra otos and just had to have them. Well, one of those two is now doing the same thing and they are not even in my resident oto's tank.
This is the disease progression: Rapidly swimming for a few seconds, followed by extremely fast breathing, listlessness, laying around the tank floor, reddened chest and then death follows usually within 24 to 36 hours. This zebra otos is still alive right now after almost 4 days but I doubt he will make it much longer. The other one is doing fine.
Today I moved the sick oto to a cycled quarantine tank (loaded with algae) and dosed with maracyn, maracyn II and Triple sulfa. I searched the net last night for possible clues or remedies and stumbled across a German webpage where I read that copper is highly toxic to otos. They were said to be more sensitive to copper then snails. Can anyone confirm this?
I have a water purification system on my tap water which should remove almost all chemicals. I therefore add Equilibrium and calcium to restore some minerals essential for my plants and snails, but copper is not one of the ingredients.
I am at a loss as to what is killing my otos.
This webpage also said that otos would love to graze on oak leaves. They advised to pour boilng water over the oak leaves which would kill off bacteria and bugs and would make the leaves sink. I tried that, but they did not sink and neither of my fish showed any interest in the leaves. Anyone done that before?