NLS = New Life Spectrum. I feed the cichlid forumla - only because I have cichlids, too. IT's all basically the same stuff. The veggie flake came in bulk from FF in a 1 lb. bag for like $10. THe brand they have is 100% vegetables, no fish meal. It's a much better food than standard "spirulina flake" that is mostly fish meal. The price is right, too.
You can get NLS on aquabid from a guy in Ohio (flydude1015?) prtty reasonably. It's expensive in the store but cheap(er) online. I usually get the 5 lb buckets for $50 or so, and they last 6 months for me with 6 tanks running. If I didn't have plecos it'd last much much longer.
NLS is great for color enhancement.
WIth those rainbows, they're used to 50-60% water changes every week - so go nuts. The only time I ever had problems with them was when I missed a water change for a week and a couple started swimming a litle weird (in circles). Getting back on track fixed it. But the best color in them comes right after a water change. They love it.k