Spirulina, being a vegetable and not meat can be refrozen, however, it is not recommended. It is better if defrosted to keep it in the refrigerator for the next day (Refreezing spirulina is a valid option).

Refreezing spirulina word of advice

Freshly frozen spirulina serves that you decided to defrost and scoop from can be placed in the fridge and be used later that day, tomorrow and even the next day. It is better to use the entire serve in your drink, however, if you can’t finish the drink simply put it in the fridge for later, finish it then or share your drink with someone. If you still want to refreeze your fresh spirulina serve you can do so.
When defrosting frozen spirulina you will notice that it turns blue. The blue pigment is called Phycocyanin.

Spirulina that turned blue

As mentioned above the blue stuff is called Phycocyanin. It is pigment-protein that does similar thing chlorophyll does only in different wavelengths (photosynthesis). Phycocyanin is a very powerful anti-oxidant and looks after your eyes, hair, brain, skin and joints to name a few. Phycocyanin is usually leached out from frozen spirulina if defrosted. The point is that even though the spirulina may have turned blue it is still good. The colour change does not affect its quality or flavour in any way.

What you visibly see is the dark blue phycocyanin colour on top of the deep green colour of the chlorophyll. Your spirulina is as good as always.

Recognize that your spirulina has gone bad

Freshly Frozen spirulina is good for a very long time, years. Once defrosted it is good in the refrigerator for about 7-10 days in the coolest place. Refreezing spirulina is not a problem, simply notice that your spirulina is now visibly blue.
To recognize that your spirulina, in the fridge, has gone bad is very simple – it will smell like a rotten egg or rotten meat. Seal it well and place it a neighbour’s bin, pesky partner’s car or boss (i.e. as far from you as possible).