The pet store operator said that gravel is a must have for cockatiels. I bought Cockatiel Gravel by Hagen. The box says it contains grit. I am concerned about the grit because of the following excerpt from this web page. "Grit is an unnecessary part of the diet for pet birds, as they do not eat anything which is difficult for their gizzards to grind up. Insoluble grit can actually impact a bird's intestinal tract, causing the bird to starve to death." Is this gravel ok to feed my birds?

Rodger