Optimal BG and Jr comes in a 40lb bag. You have to go to the "Additional Information" tab on the product you are looking to buy to see the bag weight.
I would go with the Jr for 3" CNBG. If they were HBG, the BG bag would work fine, but the CNBG's gape is pretty small for the larger Optimal BG size. The Jr would be the safest way to go since the smaller fish can use it and the larger fish will NOT refuse it, for sure.
I found myself in a similar situation my fish grew and I ended up buying a bag of the BG when my Jr was about half gone. Then I mixed equal parts to make everyone happy. Your fish will grow quick on the feed, but I think it's better to make sure all the fish sizes get plenty to eat as opposed to leaving out the smallest.
