Yes disinfect it, itch looks like they have been sprinkled in salt, salt like grains spots, it does sound like itch abit, probably the stress has caused an oubreak and with columnaris very prone to other infections, if there bad you will have to half dose or you will end up losing all the fish, don't like mixing meds, but you could lose them all, increase 02 in the water as the two meds will really take the o2 out,
Other signs for parasite infection are heavy breathing and flicking and rubbing or twitching looking uncomfortable, anyway you can take a pic to show us to see if it is itch.