The pet industry has established certain ideal ratios for balanced nutrition with regard to many animals kept as pets such as dogs, cats, and horses. For instance, I am told that dogs should have a 1.1:1 ratio of calcium to phosphate. The exact ratios for hermit crab nutrition have not been firmly established in part because their nutritional needs depend greatly on the changes in their environment (time of year, temperature, etc.) and in their own body processes (such as moulting, egg-laying, etc.).
The absence of established numeric values frustrates some crab-keepers who formulate their own homemade meals. But, for most of us, a series of numeric values to calculate wouldn’t be very practical either. We do know that protein and calcium should make up a considerable part of their daily intake and we know that certain minerals like copper and nutrients such as iodine and zeaxanthin are important to specific biological functions. The prevailing crab wisdom says that if you offer a large variety of nutritious, safe foods, then the crabs will pick and choose for a healthy balance. Since their nutritional needs fluctuate and those fluctuations are difficult to predict, having availability to whatever foods those physiological changes might require is vital. Offering many different foods is key to covering a wide range of nutrients.