First and foremost, I wouldn't bother feeding the hermits. Given the "newness" of your tank, there is still plenty of nutrient to sustain them even without a fish population at this point. If your a mind to feed the tank, do so to maintain the bacterial populations instead. In which I would use raw meaty seafoods that are less polluting in terms of what you've mentioned above. For the most part, all dried foods will contribute to this.