Ich and stress go hand in hand. A healthy fish won't get ich.
This will come from several things. To ensure ich is gone from your display tank you will need to run your tank fallow for the life cycles of ich, which is at least 6 weeks. Fish with ich can then be placed in a quarantine tank to be treated with either a copper based medication or hyposalinity.
As for what is currently going on in your display tank, can you tell us more about it? What are the current parameters? 9 chances out of 10 there is an issue going on in the water column that will require large water changes on top of the 10% weekly water changes to begin to resolve.