Unlike FBU, I don't see your main concern as pH and TA. Both ARE low but pH is 7 or more. I'd FIRST use either washing soda or borax, but not baking soda until your pH is where you want it. THEN test for TA and see if you need more. You have a vinyl pool so as long as pH is 7 or better you're oK and TA is really just not that important.

But more importantly, you need to test and maintain your FC at 15ppm. Dropping overnight to 10 from 15 means you are fighting something. BTW, pH at 7 makes the FC a bit more effective at fighting algae.