How to compensate for citric acid in hard candy? We're working on the most sour hard candy on earth. Here's the basic recipe: 2 cups sugar, 1/2 cup of water, 1/4 cup corn syrup, 3.2ml flavor (one small Lorann drum). Once the composition gets to 300F we take it of the stove, transfer into a cold container, quickly mix in 1-3 teaspoon of citric acid and pour it over a plastic mold.

The problem we're having is that the more citric acid we add to it will make it softer. Is there a way to compensate for the additional citric acid by mixing in something else? (more sugar, corn syrup perhaps?). 

It'd appreciate if somebody can explain the chemistry behind the binding of sugar and citric acid.
You are breaking the sugar into fructose and glucose, getting invert syrup

I'd suggest making the sugar base and then adding fine powder or dissolved acid with rapid cooling to stop the hydrolysis.

Or use a paste of fine citric acid with some oil to slow down dissolving of the acid.

You can also try to use mechanical mixing like extruder screw or rolls to keep the water contents lower and better control heating.

Also note that your candies can turn soft and sticky over time.