Blood worms are fine if you clean them, and keep them in the fridge to slow their metabolism. I kept them in a small tupperware with a loose fitting lid, and would strain out the worms and put in new water about every other day. If they smell, pitch em. Keeping the water clean, and cool, they will keep for about two weeks. Most problems arise from not rinsing them before feeding, or from feeding dead ones. Avoid those pitfalls, and they are a decent supplement/treat for most fish.