Will baking soda make the acid go down in your fish tank?

Baking Soda (NaHCO3) can be used in small amounts to increase the buffering capacity of water thereby binding out acidity and raising the pH.

Changing the chemistry of your fish tank is the number one mistake for a beginner. If you shock the osmotic balance of the fish by fighting acids and bases in your aquarium your fish will not be healthy. You will usually have best results when your fish become accustomed to the water that you will be using even if it is not an exact match to their natural environment.