I just bought 2 bags of 600 and, at least the first bag, it's basically the same size of 500 and my fish won't touch it. I don't understand why size is so important to them. I've tested it several times,...throw a scoop of 500 out and they won't touch it; get a scoop of 600 and throw that out, they ravish it. even the BG have no interest in 500.
