You may want to consider a second treatment. As long as you did one, it can help to insure all traces are gone. I did a second after a large 20% water change and have not see any since. I did not even get any back during my 125 break down with poor flow and lighting as I am building my new tank up.
Also, I left my skimmer off for 3-5 days after the water change as it still was going wonky... During that time I just ran fresh carbon.