The Ewer and Lucid Dreaming both help AST maintain MP. Also a caster DPS with Mana Shift can help too.

Furthermore, if your gear needs updating it's a good idea to do that, and use Largesse if your Healing still falls short. Also make sure your Tank isn't pulling too big and DPS aren't throwing themselves at AoEs or pulling ahead of the Tank.

P.S. Diurnal Aspected Benefic stacks with Aspected Helios.