Hi Brian,
I was thinking the vitamins might be causing a reaction until you said the other birds get them too I will say though, your hygeine standards are to be congratulated Your birds are lucky to have such a good keeper. You could try the old process of elimination, start replacing or changing things one at a time and you might be lucky enough to stumble across the cause. Wish I could be more help Brian, goodluck
Gordon...

Thanks Gordon ... I stopped the vitamins yesterday to see if that helps. If that doesnt work then I'll try eliminating other things to see what's causing it. I'll let you know what happens.