I have a 65 gallon system, medium bioload, and I have an asm g4 "rated" at 350 gallons. A skimmers "rating" really means nothing if you look deeper into it. If your tank seems deprived of nutrients, feed more, or dry up the foam. Most people that have 150 gallon displays run skimmers that are "rated" for 300-500 gallons if you look arround in people's build threads.