Allow it to come up to room temperature before opening,
otherwise moisture will condense on it, greatly
reducing its storage life.

Spirulina is not a good supplement.

Quoting from "Vitamin B-12:  Plant Sources, Requirements,
and Assay" by Victor Herbert, _American_Journal_of_
_Clinical_Nutrition_, 1988, volume 48, page 857:

"Vitamin B-12 is of singular interest in any discussion
of vegetarian diets because this vitamin is not found
in plant foods as are other vitamins.  Confusion about
what sources may yield vitamin B-12 to strict vegetarians
has arisen because the standard US Pharmacopeia (USP)
assay for vitamin B-12 does not assay only vitamin B-12.
In the USP method the content of vitamin B-12 of any given
food is determined by making a water extract of that food
and feeding the extract to a bacterium (_Lactobacillus_
_leichmannii_).  The quantity of vitamin B-12 is
determined by the amount of bacterial growth.  The problem
is that what is active vitamin B-12 for bacteria is not
necessarily active vitamin B-12 for humans.  Many of the
papers in the literature give values of vitamin B-12 in
food that are false because as much as 80% of the activity
by this method is due to inactive analogues of vitamin
B-12."

"We studied several types of tempeh, including Original
Soy Tempeh, a _Rhizobus_oligosporus_ culture with a label
claim of 160% of the US RDA for vitamin B-12 per 4 oz.
Using the differential radioassay we found there was
practically no vitamin B-12 in it."

"We also studied most of the spirulinas sold in health
food stores as sources of vitamin B-12;  there is
practically no vitamin B-12 in them.  The so-called
vitamin B-12 is almost exclusively analogues of vitamin
B-12 and we have extracted the two largest peaks of
analogues and they actually block vitamin B-12 metabolism.
We suspect that people taking spirulina as a source
of vitamin B-12 may get vitamin B-12 deficiency quicker
because the analogues in the product block human
mammalian cell metabolism in culture and we suspect
they will also do this in the living human.  Remember
that the label claim of vitamin B-12 is actually a
claim of corrinoid content, not vitamin B-12 content."