Abstract: An aerator particularly useful in the aeration of waste treatment systems. The aerator has a hollow support pipe communicating air to arms having diffuser stones, the support pipe extending upwardly from a weighted base. The diffuser stones are near the ends of the arms. A first pair of arms is lower than a second pair of arms and each pair of arms has a common axis. The axes of the arms are angled relative to each other. The diffusers on the lower pair of arms are angled upward and the diffusers on the upper arms are angled downward. The aerator provides a large projected area for the diffusers as viewed from above, and spreads air bubbles laterally away from the aerator. The aerator of the present invention keeps the diffusers above the bottom at an optimized height while maximizing aeration.