quarantine after ich?

this is a query in the aftermath of a sad story - a month or so ago I
bought five baby (very baby) botia striatas and two female dwarf
gouramis. They'd come from a shop with a common filter system (and I
only have one spare tank) so I kept all seven fish in the same tank to
quarantine them, and treated with protozin at half strength as a
prophylactic. a week later, two striatas were dead. I kind of assumed
(after discussion with some loachy people) that they were very small and
undernourished from transport and that it had all been too stressful for
them. Next day, the other striatas were spotty. Sigh. To cut a long
story short, on Monday morning I found the last striata dead (I have a
feeling it was the protozin that killed him in the end, not the ich
which had I think just about cleared up).

My query is, how long should I wait before adding the gouramis to the
main tank, which contains a male dwarf gourami some rasboras and some
(slightly random) kuhlis? One gourami had two spots a couple of weeks
ago and has shown no signs since, the other has been consistently clear.
I'm extremely reluctant to add them at the moment, as this is the first
time I've had a disease in a tank and I would hate to infect the kuhlis,
not least because one is rare in the hobby (I haven't even managed to
find a photo of another one on the net).

any advice will be very gratefully received.
--
sophie

www.freewebs.com/fishstuff
(under construction. ish.)