Sounds like it's too big for their taste. Usually, for something softer, each time they spat it out, the food split and become smaller. After a couple of spit, if the size doesn't change, they give up on it. In that case, I usually just feed them a smaller size food. Do you have a small food processor? Put some in there and give it a quick split second chop. You should be able to get some smaller size pellets.
I have 5 different sizes of sieves. I top coat some big pellets by mixing some extra nutrition powder and mix with a food processor. Then I use the sieves to filter me 6 different sizes of pellets to feed baby fish in different stages.