Smelly tank

[Coralgurl]

Seems like it's coming from the display tank, sump isn't that bad. I moved one of the power heads down a few inches to try to move more flow over the sand and I'm seeing more solids floating around, had to look closely to make sure it wasn't bubbles.

Mentioning a dead snail, I added 20 sand snails but haven't seen a single one come out....could they be causing this if they are dead??