I have a bag of 500 and a bag of optimal BG. I have mixed them together and they are eating both fine. They like the Optimal better, it seems. The pellet size of the 600 is bigger and closer to the pellet size of the Optimal. I am thinking of getting 600 the next time I get a bag for the bigger pellet size. I have noticed that my hybrid crappie seem to come up for the 500 better.