The problem with fatty deposition is that typically the fish will be dead before one actually sees a physical change in the fish. The damage (necrosis) is internal, sometimes even leading to secondary infections due to a suppressed immune system. So saying that "I can't see any difference", or "my fish all seem fine", is a rather non scientific approach to what is commonly referred to as fatty live disease. Some of the nations leading experts on fish nutrition (Juli-Anne B. Royesa, Ruth Francis-Floyd, et al) have stated:
Fatty infiltration of the liver has also been designated "the most common metabolic disturbance and most frequent cause of death in aquarium fish"
