I would never give mine Tums, though Tom would be very happy of it I am sure!
What could be really good is nature Yogourt. My grays love it. What is great with yogourt is that the bacterias that transform the milk into yogourt digest the lactose in it, so there is almost no lactose. It is OK for birds, and full of calcium. You can even use probiotic yogourt. The bacterias in it are the same that are used in the probiotic mixes given to birds
Hubby was giving regularily milk to Tom, in quantities that should have given him diarrhea. But no diarrhea at all. It puzzled me a lot, until I understood that the probiotic bacterias colonized his intestines and digested the lactose for him. Cool, huh?