Hello! I recently ordered a bottle of Seachem Prime water conditioner. It came in today, which is my water changing day. One of my guppies has been acting lethargic and slow recently, but about five minutes after I added the conditioner, he perked up and swam around. He even played with the filter current at the surface, which he used to love to do. This stuff is amazing! I have noticed that there is a slight sulfuric smell, should I be worried? What causes it? Ammonia 0, nitrite 0, nitrate 2.5 ppm.