One of my metallic Koi was looking slower than normal so I've netted him &
he's got a bad dose of fungal infection. I've treated & isolated him (in a
small 20 Gallon plastic box) & treated the pond.

He's through the 1st night but the rot / cotton wool has got to a lot (30%)
of his scales.

Question is, how long before reintroduction - is this a period of days,
weeks or months. Do I wait until he's 100% back on track with all signs of
infection gone, or will the isolation stress him out even more? What about
repeat treatments?

Thanks