Buy this iron product at Walmart, has Ferrous Sulfate and calcium carbonate ingredient in it, but this two ingredient interact each other on many web site, I wonder can let me exchange other iron product with lowest mg unit, I open the seal little hole, slite one tab out , so Walmart wont let me exchange if open, please help. my name is kim hua address : 6803 bitterroot Austin TX 78744 phone: 512-925****