Couple of points:
1. There was a bad run of ozone lines recently in the industry and there was an oil in the ozone line that was causing the water to be exceedingly fizzy. After, say, 5-10 mins or so, the microscopic bubbles would dissipate completely. The water didn't foam mind you, so if you're having foam issues, a defoamer may work. However, if you're having symptoms as described above, you may need to run a gallon or two of vinegar in your spa (while having all jets open, all air off, and your cartridge pulled out) for an hour or so, and then drain it.
I have Catalina Spas as one of my brands I carry but I have heard of other brands in the industry having the same issue with fizzing and it was all traced back to oils in the ozone line.
2. pH being low: Usage tends to drop your pH level. Be sure to have your alkalinity level balanced and that will keep your pH in line longer. Sometimes, when increasing your alkalinity level, you will see an uptick in your pH level as well. Thus, if your alkalinity is low, adjust that first and after an hour or longer, retest your pH and adjust if necessary.
I dislike Sodium BiCarbonate as it will bring up both pH and alkalinity (Yes- I know in my previous statement I indicated your pH can rise when adding alkalinity increaser but bear with me). Sodium Carbonate is specifically for pH increasing and Sodium Hydrogen Carbonate is specifically for increasing alkalinity. The BiCarb will bring them both up. Sometimes you only need one to be raised, not both.
Does this make sense? I hope I didn't make a mess of this explanation.
Good luck moving forward.