I used to feed my fish with life food such as tubifex, boon (daphnia) and bloodworms.
Then I found that many lfs do not sell these live food. Some friends told me feeding live food carries a risk of parasite and hydra attack on the fish, and many of them end up feeding their fish only with dry fish food like pellets and flakes. I myself have experienced many times fish dying one by one for no apparent reason, which is very heart-breaking when we treasure our expensive pet fish very much. I suspect the fish were attacked by either parasites or hydra. When I changed to feeding them only dry fish food, I never had one fish died. And because of that, I have stuck to feeding my fish only dry food always.

The questions I want to ask is

1)how to keep dry fish food fresh for a long time?
2)Is expired fish food safe for fish?
3)How to tell whether the food is still good?