Have you noticed what else is going on around your aquarium when your foam tower colapses? With my EV-180 if we are cooking in the kitchen especially with greasy foods like bacon the foam tower will collapse. It also collapses after I have been working in the tank or feeding.
Keeping the tower and the collection cup clean increases the efficiency of this skimmer, the foam production will slowly decrease as skimate accumulates on the sides of the skimmer tower. If you are getting large quantities of skimmate collecting on in the tower and the throat of the collection cup you may be skimming too dry, if this is the case try increasing the height of the water in the reaction chamber.
