1 week is not enough time to be 100% that all the ich organisms are dead. I would treat with medication exactly as per the instructions for at least 1 more week.
Then, you need to treat the tank like it is in quarantine for at least another 6 weeks to be sure that there aren't any reoccurrences.
And, finally, when you do bring more home, you need to quarantine them for around 6 weeks as well to see if they develop any issues as well.
I know that this is a long time, but to help pass the time, I suggest you read and study this:
[URL="http
/www.skepticalaquarist.com/docs/health/ich.shtml"]http
/www.skepticalaquarist.com/docs/health/ich.shtml[/URL] it is by and far the best document about ich that I have ever found on the Internet. Talks about a lot of the misconceptions and truths about ich.