i would think you would need a stronger pump if it was aero but I dont know much about aero. I use a 1/4hp chiller for 100 gallons of water and it lowers it 25 degrees F no problem. I would think a 1/10hp unit would cool 40 gallons. Obviously I use an entirely different system and more water but I use a 500gph pump. Maybe the pump is too fast for the chiller? Can you hear it going on?