Do you have a QT Tank for one? If so move all fish to the QT and treat.
Do not add or change anything to the main tank for about 3 months after the last sign of the virus being in the main tank. This includes keeping the previously infected fish in your QT tank.
The effectiveness of the above listed steps is a topic that is highly debatable as the only guaranteed way to get ich out of an infect tank, is to leave sit without any fish for a period of about 3 months while maintaining higher temperatures in the tank.
Effective Treatments:
Based on my experiences and research, the below are the two best treatment options for treating a infected fish. Please keep in mind that it is not recommend to try these treatments in your main / display tank. Also, as the ich virus is actually in the skin of the fish, fresh water or medicated dips will most likely not be effective enough to properly treat the ich. Treatment in a quarantine tank remains the most effective approach. NEVER combine any two of these below methods (or any other methods) when dealing with ich. Pick the best suited method for your situation and use only that one.
1. Copper Based Medications: This is my preferred approach. I have had very good success with using a quarantine tank and treating with copper meds (like Coppermine by Seachem ) by following directions on the bottle. After using the meds as directed, I will remove the meds from the set-up with a few large water changes and running carbon. If the ich is gone I will keep the fish in the QT tank for another 3 or 4 weeks just to make sure. If it appears that the ich is not gone, I will treat again followed by a 3 to 4 week observation period as well. The biggest drawback to this treatment is that some of the more sensitive fish may not be able to handle copper based meds (like mandarins). Other treatments will have to be used for those fish. Copper based meds can kill inverts and corals (even in trace amounts) so it is not suggested for use in your display tank. I would also suggest getting a copper test kit to ensure the level is maintained at 0.2 mg/l as higher levels start to become toxic to even hardy fish.
I have tried other non-copper based meds but found them not to be effective to break the ich life cycle and cure the fish of the infection.
2. Using Hyposalinity – This method involves using a QT tank with no meds, only lowing the salinity to 1.008 to 1.009 (11 to 12 ppt). This needs to be done slowly never lowering the salinity by more than 0.004 within a 24 hour period. You will need a high quality / accurate refractometer for measuring your salinity. Once the fish has lost all the ich spots, slowly rise the salinity to it normal level just as you have done to lower it. Keep the fish in the QT tank for 3 or 4 more weeks to make sure. The biggest drawback of this method would be keeping your pH stable. I have not personally tried this method, but a friend of mine swears by this approach having used it many times with very good success.