Most surfactants (and the dishwashing liquids that contain them) are influenced by pH. When you adjust the pH of your bubble juice to the optimal range, the bubble juice tends to work better and less detergent is required. This impact is especially noticeable with Japan's Charmy where adjusting the pH can double (or more) its bubble-making efficiency.
Baking powder or baking soda+citric acid can gently lower the pH of bubble juice. It appears (as of Fall 2013) that these additives are providing their benefit via pH adjustment as they can lower the pH into the target range (usually 7.0-7.6) without over-acidifying the juice. Most bubble juice seems to suffer if the pH is lowered too much.
MORE INFORMATION COMING SOON!
See the various articles and blog entries in the pH category for more information.