Thanks. Makes sense. Never thought about the PH or even salt content. I think I may just try a small batch with the store bought tomatoes and see how it turns out.I think it would work but the quality might be off.
One of the issues in canning both tomatoes and salsa is being sure that your pH is safe. Starting your salsa with canned tomatoes will have a different pH than with fresh tomatoes as they've already been canned once. Unless you're able to accurately measure pH I don't think it's worth altering a recipe because of the safety risk. Now yes. using canned tomatoes will make the salsa more acidic most likely which is the direction of safety, but the resut might be too sour as well.
When someone hands me a jar of their custom home canned salsa, i always just compost it. It's not worth the risk to me unless they followed a developed and tested recipe.
I would like to make (can) some more quick and easy salsa. However, tomatoes are not in season. Can I use fresh peppers and onions along with canned tomatoes and process them ok?