Chaetomorpha Macro Algae
Fast growing and isn't a tank crash risk like Caulerpa (It can go sexual and spread through the whole tank!). See picture for representative size (XL Frag plug provided as reference).
2017 Update: We now typically ship 2-3x more macro algae then previously, for the same price! We grow it rapidly in our systems so get in touch if you'd like to order larger quantities.