The rotten egg or sulfur smell is very common in amquel,novaqua, and its the worst in prime. Its just part of there chemical makeup.
As Sodium thiosulfate and purified water age together they start to give off this sulfur smell. ST and purified water are the main ingredients in every aquarium water conditioner.
If the smell bothers you switch to Aquasafe. It contains the sodium thiosulfate as well but for some unknown reason it does not give off the rotten egg (sulfur) smell.