It would be a good idea to increase the pH slowly, use 1 gallon of tank water as a test to see how much you'll need to raise the whole tank. It will most likely take a week or longer to stabilize the pH enough to keep it from dropping back to the original level. Keep dosing every 24 hours until the pH is where you want it.
Baking soda will only raise the pH to 8.4 max, regardless of how much you dump in. Using more will raise the Kh (carbonate hardness) which determines the buffering capacity/stability of the pH.
Sodium Bicarbonate is common in the hobby for increasing kh and pH. According to what I've heard from another local hobbyist, it breaks down quicker than other sources, but I haven't done any testing or looked into it further. It's listed as an ingredient in the rift lake buffer recipe in the library.