That seems to me a lot of fish for a 55, and my hunch is the stress of the move combined with the drastic change in quarters will result in fatalities. Do you run a UV? Achilles are particularly suysceptible to ich, as you no doubt know.
Removing only some of the fish is not going to eradicate the parasite entirely from the system.
If it's been a year, as long as you keep the fish otherwise healthy, I don't see why it's a concern, unless you see a visibly bad infestation.
Anyway, I'd add a UV if you don't have one and perhaps try a medicated feeding regimen when you see some evidence of spots.