any powdered spirulina - go cheap.
I can harvest 2-3x day each tank IF I'm keeping my salinity low (around 1.020). For me, evaporation continues to be my biggest challenge.
If you want to harvest pods for sale, Hans uses my method but big bins outside and in his garage... but I refer to this method as 'dirty' because you'll catch spirulina in your nets when you catch pods... I learned he lets them settle and does a recatch or something so he can then sell pods locally using the spirulina method. He also cultures phyto. I think pods enjoy phyto but I'm too lazy. My pods only get phyto as an occasional treat.