I used to use potassium hydroxide solution to adjust pH. *You could use some calcium hydroxide to do the same.. Probably easier to get through the aquarium trade. *I would not use baking soda which is sodium bicarbonate. *In any event you should first test your pH after you mix up a batch of diluted fertilizer. *You might be lucky and find it is fine.
The use of a calcium component in potting mix, while adding some calcium which the plant needs, is more for neutralizing acidic potting mix. *I think in the case of some Paphs it has been shown to be helpful because it maintains the neutral to (in some cases) slightly alkaline root zone. *I know the Wellensteins use a crushed oyster shell in these instances. *They also use a balanced fertilizer with calcium and all other macro, minor and trace elements. *The fertilizer and the crushed shell serve different purposes to the plants health.