I have tested pH prior to and after adding baking soda.
30 gallon tropical tank at 85 degrees, pH = 6
added one heaping teaspoon (1/2 tablespoon) and it went to 8.5
Water change is usually a better option, yet in an emergency...
DON'T PANIC! Be careful!
Yeah, I know 85 is a little hot for tropical, but no AC
here in Ohio land and ambient temperature is driving heat in the tank.
FYI, my spotted cat had "submarined" and tipped me off to the low pH.
The disc, barbs, danos, hatchets and pleco all seemed happy enough.
BTW - those of you with pleco's and disc's - beware of salting!