Have you kept it Refrigerated?
on the DTs website...
"D. Mortality: While in storage a small percentage of the cells will die. In recent testing of DT’s Live Marine Phytoplankton, more then 90 % of the cells were still alive and intact after 13 weeks of storage. It is reasonable to assume that by the “best if used by date”, based on a 5 month shelf life, less than 15 % of the cells may die.
Any odor from the phytoplankton is most noticeable in the air that is trapped in the bottle, and it builds up over time. That is why a half empty bottle smells more than a full bottle, and a large bottle smells more than a small bottle. To remove the old air, squeeze the bottle until the phytoplankton is at the surface. While odor intensity is almost impossible to describe; it is normal for some odor of sulfides to be detected, particularly in DT’s that has been in storage for a while.
If a significant amount of the phytoplankton is dead, the intensity of the odor will be so strong that it is unlikely that anyone could stand smelling it. "