Dr.Bruce, Tare n. is the weight of packaging minus the weight of the product. Tare v. is to weigh packaging to calculate the amount of tare to be deducted from a particular cargo. It is often used in weighing to zero out the scales before a particular item is weighed. You mentioned that the Wal-Mart scales had a zeroing feature.
Your fish are impressive. I am very hopeful that Cecil & I can complete the trip to your fish ranch this spring.
When trying the soft pellets method maybe try making a very stiff damp paste with the natural food-pellet mixture before you go to the fish barn. Amount of dampness is critical. Think of it as similar to filling a tooth. Too moist of packing will not compress properly. If you have it dry enough with several hours of aging, the mixture should be able to be molded and not stick to your fingers similar to pie dough or play dough. Mash or smash the soft pellets and mix in desired food pieces. NOTE - wet food pieces could cause the mixture to be too moist. Form the whole combination into a ball. Pinch off and mold soft pellets into a similar size as the pieces of chopped worms.