Fish food pellets - how long are they good after opening the jar?

[RD]

The amount of nutrient loss in 6 months time would depend entirely on how they are stored.
If stored in a cool, dry, dark environment, the overall nutrient loss would be minimal, and there is certainly no reason to be tossing them out.

[fishoholic]

Since you said the fish are spitting them out, I'd get new ones.

[Murminator]

Clowns always like to play with their food when they are not hungry....they will suck them in and spit them out several times