Well saying your parameters are 'fine' doesnt mean very much. Can you provide more exact numbers in addition to your water change schedule? Do you know what is in this food and its nutritional breakdown (namely protein & fat levels)? By 6-12mths, she should started hump development. Lack of sufficient wcs leading to hormonal inhibition, excess nitrate levels and insufficient protien/fat in the diet are all factors behind lack of hump development. Are the wens on your orandas growing well? Does the ryukin get her share of food? We need to do some detective work here to figure out what the reason behind this is so lots of questions!