My favorite was HBH super soft spirulina, but I believe they have gone out of business, so I have switched to NLS Algaemax, and Kenfish veggie pellets.
I use Omega One Super veggie pellets and flakes if extra vegetable matter is needed. However, Kelp is the number one ingredient and spirulina is number two. My Uaru eat it up but there is very little, actually nothing, they won't eat.
Alright jaws! I was just wondering about this myself. Once in a while I I throw algae waffers in my community tank for a snack, and I swear it immediately brings out more color, specifically blues and greens. I have been adding Zoomeds Spirulina 20 to my flake mix bc it's cheap, I'll check out the others now also.