What did it crash from? Certainly not lack of oxygenation unless his pumps were at the bottom of the tank. Properly placed power heads at the surface create more gas exchange than virtually any other component in a system.DannyBradley;61998 wrote: 4. I've seen tanks with plenty of flow from powerheads crash when the main system was off. One of my clients turned off his system to feed his sea horses and left his office for the night without tunring it back on. There was still a 5X turnover in the tank from powerheads. He lost 90% of his livestock overnight.