Hey Mary - to answer your question, using a little sprinkle of Ag lime (calcium carbonate - CaCo3) every now and again would be just fine. You wondered about "Tums" - they would be fine I'm sure, but definitely more expensive than lime. Just make sure whatever you use has a high percentage of calcium carbonate (absolutely DON'T use "builder's lime" or "slaked lime"). Dolomitic lime would also likely be just fine.
Mary look up Wood Worm Farms near Montreal, Quebec. It's where I purchased my EF worms, along with a wood stack tray system. The EF worms from that guy were in superb shape when they arrived in the mail. So I have no problem recommending them. He should be ready to sell worms right now, according to the last email conversation I had with him about two weeks ago.