Doing a water change has nothing to do with treating for ich. The purpose was to reduce the medication in the water. I stress this again: have you read all of the ich stickies on the top of this forum? To treat ich you need to set up a quarantine tank and apply either copper or hyposalinity. Your puffer sounds like it's in a bad condition and at this moment, its immune system cannot defend the ich attack anymore. You will have to set up the QT, put all of the fish in there, and apply one of the two treatments as soon as possible, or I'm afraid your puffer won't last for a few more days.