I have a spillover spa and 2 waterfalls (and a few deck jets and bubblers) and I have NO foaming and have been using Borax for a while now at 50 ppm! (I'm the one that started The Great Tetraborate Experiment in the China Shop!)
Your foaming is NOT from the borax. What is your calcium hardness? How high is your FC? Post a full set of test results and perhaps we can figure out why your pool is foaming. Are you sure you are using 20 mule team borax in the green box and not something like Boraxo (which is a soap)?