Richard's given you good advice.

Your CYA at 50 is fine, but I consider that the high end of the ideal range for our area (I'm in North Central NJ). I would NOT use Tri-chlor pucks at this time unless you must.

VERY IMPORTANT!!!!! NEVER, NEVER, EVER PUT ANYTHING IN YOUR AUTOMATIC FEEDER BUT TRI-CHLOR PUCKS! ANYTHING ELSE IS AN EXTREME SAFETY HAZARD!!

If you continue to use pucks, as Chem_Geek said, your CYA will rise to levels that require MUCH higher chlorine levels. Tri-Chlor is also very, very acidic, which explains your pH of 7.0. With vinyl, 6.9 is the minimum. Below that the acid may begin to degrade the vinyl.

Baking Soda does not raise pH significantly but it does raise Total Alkalinity (TA).

All Chem_Geek was suggesting was that since you need to raise both pH and TA, you can use Arm&Hammer Washing Soda (in the Yellow box) rather than using both Baking Soda and Borax.

Why would you do this? Generally, pound for pound, at the supermarket Washing Soda is a little cheaper than Borax. But more importantly you only need to add one chem to get both effects.

99 times out a 100, I'll use Borax to raise pH, especially since I'm generally facing higher TA levels (140 or so--which is fine in vinyl pool with no heater). Borax won't increase TA levels, sort of. Washing Soda will. (as pH rises and falls, TA goes up and down with it. W/S raises the TA more than the pH rise does alone.)

So the other day my pH was 6.9 (VERY unusual for me) and my TA was 50. IDEAL conditions for using Washing Soda rather than Borax and Baking soda.

Oh, that base demand test (and the acid demand test) are virtually worthless, even in the 2006. You will figure out very quickly how much of each chem to add. With your pool (40,000+ gal), and your pH, I'd start with 2lb of Washing Soda, wait a couple of hours and check again. If you use Borax and Baking Soda, I'd start with 2 lbs of Borax (Half a box) but only one pound of Baking Soda. Lowering TA is a pain in the neck--all the way to your ankles--so it's far better to go slowly and approach your target gradually.