tropic eden reefflakes are the go to. i went with the miniflakes (1mm smaller) and they do work but can get blown around pretty easily depending on where your powerhead is. some people mix different sizes together. tropic eden sizes:
Grain Sizes Available:
Aragasnow - 0.5mm
Tonga Special Pink - 0.8mm
Miniflakes - 2.0mm
Mesoflakes - 2.7mm
Reefflakes - 3.0mm