That's right. Total Alkalinity is kinda mis-named--it's a buffer or stabilizer for pH. You raise it by adding baking soda. Your pH at 7.8 is at the top of the acceptable level--and your chlorine is a lot less effective there than at, say, 7.3, which is also acceptable.

You should raise your Tot Alk to at least 100--and lower your pH to 7.4-7.6. You'll see Tot Alk go down a bit then, but you you can raise some more. 100- 125 is perfect for Tot Alk and your pH shouldn't move so much.