No, you don't have to add any kind of acid. Tomatoes are very acidic to begin with anyway. A good thing about doing it yourself is that salt is optional in home-canned vegetables. You don't even particularly need to buy the mason jars, you can use any glass jars that you have left over from pickles or something. Start by washing the jars with soap and water and then sterilizing the jars and lids in boiling water. When filling the jars leave headspace between the jar rim and the liquid. If you do buy mason jars there is a chart included to tell you how much space to leave, but I'm sure you could find it online somewhere. VERY IMPORTANT STEP When closing the jars, remove trapped air bubbles before tightening the lid. Run a non-metallic spatula along the inside edge of the jar. Move the spatula up and down along the inside wall to release air bubbles. Add more boiling liquid if needed. Wipe the jar rim with a CLEAN damp paper towel to remove any food particles. Checking Seals and Storing Listen for the familiar "ping" as the jars cool. Look for the slight depression in the lid's center. Remove the ringbands, wipe jars with a damp cloth, and add labels. Store in a cool, dry, dark place. Signs of Spoilage If a jar does not seem completely normal before or after opening, do not use. This includes leaking jars, bulging lids, and jars that spurt when opened. If the food looks spoiled, foams, or has an off odor during preparation, discard it. It's really not difficult. Just remember two things, no air and make sure everything is clean. Good luck!