When choosing Spirulina, make sure to choose one that is organic, as others can be contaminated or have nitrate compounds as additives. The one currently using can be purchased here.
It does taste like pond water though, so many people prefer supplements like this high quality spirulina capsule.
You can also mix into water and drink straight, though many people have trouble with this. The phosphorous makes it useful for the tooth remineralizing regimen, and it is best taken with an Omega-3 source.