I've been running AC500's for 5 years now....No complaints from my end.....I probably will always have a few 300, 500's cleaning something in the fish room till the end....The AC's are as simple as they get.....I've use them on cycling tanks and breeding tanks....No matter what the main filter was, I always had a 300 or 500 pumping away in the bak of my larger tanks(100+)...