Hemp comes out of through their vent looking like the 'prepared' stuff that's introduced to the water. They consume small water snails, and they don't soften. Also, surely not all sand/fine gravel gets expelled through their gills when they're feeding. Larger indigestible items (inc. those too big to travel through their gut and out of their vent) will be ejected through their mouths/gills. They manage 'donkey chokers' ok, so I don't think (the much smaller) hemp particles are any threat to them. (All IMO)I don't think it matters provided all the grains have softened. Never tried hard grains, but I would be concerned about the fishes welfare if there were lots of hard bits.