Bill wrote:
On Wed, 19 May 2004 22:13:15 +0000 (UTC), Cichlidiot
wrote:

Well, this is a case of knowing where people are coming from. In the case
of black spot disease, it would be of concern to pond goldfish keepers,
because, being that ponds are outdoors, all the vectors required for the
disease (snails, birds, fish) are present. This is not a concern to the
indoor tank keeper, unless for some reason you have birds free-flying in
your home. It is possible that some goldfish keepers have experienced this
in their ponds, polarizing them against snails, even in situations were
there are no birds present. Note particularly that the page referenced
does not even mention the role birds play in the lifecycle.

The bird factor can indeed affect indoor aquaria. A store bought
plant can come from suppliers that use outdoor growing ponds. Plenty
of birds there.

Okay, so I'm reaching.

Well, let's evaluate this for a moment even though you say you're
reaching. The life cycle of black spot is as follows. The adult lives in
birds which pass the eggs in their feces. The eggs that land in water then
hatch and inhabit snails. It goes through some larva stages while living
in the snail then develops to a stage that infects fish, the black spot
"disease". The fish is then eaten by a bird, where the black spot parasite
develops into its adult form.

So, assuming that you got infested snails on your plant purchase, then you
could see the black spot on the fish. But, unless you are constantly
introducing infested snails, without the bird to carry the adult form, the
life cycle is interrupted and the black spot infestation is self-limiting.
You could also do any of the techniques to "de-snail" new plants to
prevent the snail vector.