What types of fish are left? What kind of substrate and plants/decorations are in the tank? What medication did you use? Have you done any water changes?
I ask all of this because it makes it easier to suggest helpful treatment options. Skai did a good job answering but there are some things that need to be looked at as well.
Ich lives a part of it life cycle in the water and if not removed can "re-infect" the tank. You remove the ich by water changes and vacuuming your substrate. Ich is a parasite and what you're seeing on the fish is the encysted stage (also the only stage that is visible to the human eye) and medication does nothing to the encysted stage because the medication can't penetrate that stage. The medication can kill of the free swimming ich in the water. So you may have another outbreak if the encysted stage came off after the medication.
I beat ich not that long ago as well. My tank was smaller but I removed everything from it and did water changes like crazy with small amounts of aquarium salt added with increased heat. From what a lot of the more advanced aquarium owners on here will tell you is that medication may or may not work but heat will work as long as you don't have a heat resistant ich strain.
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