The important thing to remember about taking supplements to relieve the symptoms of GERD is that anything that neutralizes stomach acid, such as calcium supplements in any form, ultimately makes the problem worse. In fact, it's actually helpful to increase stomach acid if and only if you take the an acid-producing supplement (1) before a meal and (2) you can discipline yourself not to overeat.
One supplement that stimulates the release of stomach acid is betaine. As its name suggests, betaine is derived from beets. It's basically the “bitter” in beets, and like any bitter food, betaine activates a reflex that tells your stomach to release more of its own acid. Take just one tablet about 10 minutes before a meal. You may feel a slight warmth in your stomach. That's a sign that the product is working. Then eat a plate of food and wait to see how you feel an hour later. If you don't have any signs of GERD, then you can cautiously repeat the product the next time you eat. Stop taking betaine at the first sign of GERD. It works by helping your stomach complete digestion and kill the bacteria that cause overgrowth in your small intestine.
A product of similar benefit is artichoke extract, which is also bitter. Artichoke extract also stimulates the release of stomach acid, which, ironically, helps food go down rather than come up. Always take artichoke extract before a meal, and don't cancel out its effects by overeating.