Also do 10 - 20% water changes daily. Consentrate on the bottom of the tank more when you do the water changes. At one point in their lifespan the ick are at the bottom of the tank or free swimming. Pullling the water out pulls out some of the ick with it. Just remember this pulls out the salt along with it. So treat the new water with salt before you put it in. Meaning if you have a 5 gal bucket treat the recommended dose for 5 gallons.
I also wouldn't worry about quarantining now, treat the main tank.
It'll take a couple of weeks of treating before ick goes away.