Calcium deposit cleaning on the potty area may be done using vinegar and water. We suggest to rinse this thoroughly with luke warm water to avoid residual sour smell. Avoid soaps as calcium makes it is less efficient cleansing agent.
With regards to hay intake on rabbits, hay are integral part of a rabbits' diet for proper functioning of their digestive system. The product you made mentioned are ideal for the age of your pet, hence we suggest to provide appropriate amount of food based on your pet's body condition.
In relation to weight, it varies since usually assessing the body condition whether fat/skinny is an important criteria for adjusting the amount of food. We suggest further to have a regular veterinary visit for optimum assessment of your pet's health.
With regards to proper burying procedure of dead pets, there are ideal protocols promulgated by National Environmental Agency on dead pets (http://app2.nea.gov.sg/topics_waste.aspx
) or alternatively you may contact your veterinary clinic of choice for burying/ cremation services.
With warm regards,
Eliezer M. Bauzon, DVM RN