If your protien skimmer is a hang on, and you have just added phytoplex or calcium, it is best to turn your skimmer off for a few hours. You might also notice your skimmer is spurting out mini bubbles during this sudden additions of chemicals. This is because many of these additives raise the amonium for a short time (only by very little) and the protien skimmer is seperating them from the water. This same thing happened to me when I first bought a skimmer, and i just read the FAQ's that came with the box and it explained it all. Its amazing what a little simple reading can do.