Oh, this is fun!
PO replacement with calcium carbonate is always a good choice. By the way, what is the pt's albumin? Remember to correct the calcium for low or high albumin... for every 1 mg below 4.0 of albumin add 0.8 to the calcium or for every 1 above 4.0 decrease the calcium by 0.8. Often what appears to be a low calcium is actually in the normal range. If still in doubt get the ionized calcium.
Calcium gluconate is good for when the pt has hyperkalemia to stabilize the myocardium, but not good for raising low serum calcium levels.