What Concentration Of Acid Do To A Shell

We had started our experiment by learning about the change in the earth and what it does to the concentration in the oceans water. When global changes occur, they don’t only change that one thing it changes many things. Such as concentration in the water. For example, when heavy machinery or facilities burn fossil fuels, which releases more carbon dioxide in the air, the ocean sucks it up and the acidity in the water completely changes even if it goes up by .1 or .2 percent it’s still a lot and will affect all the life in the water. Our guiding question to the experiment was, what does different concentrations of acid do to the shell? I had hypothesized that when we increased the amount of acid in the water the mass of the shell would decrease.
We had three cups of water with the same amount of water in it and we added 3 different amounts of vinegar in the cups, we had then grabbed three shells that looked similar and had looked like they had almost the same mass we then weighed them took down the data then dropped the shells into the water and waited 6 days. When the six days were up we took the shells out dried them and then checked the weight after being in the cups for 6 days. When we measured the change, we had a few different results, when we measured them the two cups with the more acid added had a bigger change but when we checked the weight of the shell with ¼ teaspoon in it had no