IMHO, I believe it depends on your WC sched and filtration. Per norm, you would be at the overstock now, but if the right conditions are present, you would not need to upgrade yet. BN cats can not be sexed until they are around 3 inches in length as they begin to show their bristles, and for that it takes quite a few months, I've had some take 9 months before I could tell.
HTH