Don't worry about the alkalinity and calcium . . . at all. Just leave them alone.

Go to Lowes or Home Depot and get some stabilizer -- 3# is enough, though you'll probably have to buy more -- and a gallon of muriatic acid.
+ Put the stabilizer in an old long sock, tie the open end in a knot, and then use some twine to hang the sock more or less in front of the pool return.
+ Add acid, a small glug at a time (maybe 1/2 cup) as needed to keep the pH down. WEAR GLASSES and GLOVES, and watch out for the fumes.
(If you get it on you, rinse it off in the pool; if you get it in your eyes, flop over in the pool and open your eyes after you move away from the acid you dumped. Do NOT take the time to get to a 'clear' water source; do NOT spray water from a hose into your eyes -- you can put your eye out that way!)
+ Store the muriatic acid inside a small plastic bucket or trashcan. If you've got a tight lid for the can, use that; otherwise put the acid in a garbage bag and close it up. Do NOT open the bag / can inside. Carry it outside before opening -- the fumes are no fun.

Use borax if your pH gets too low. Other than that, add bleach as needed.

Once you get the stabilizer in the water, you should be able to dose every other day, instead of morning and evening.

BUT TO ANSWER YOUR QUESTIONS:

1. The pool store goop will help fill your dealer's wallet, but won't help your pool much: good filtration does NOT come in a bottle!

2. As long as the walls are not slimy, the water is not green and the chlorine is above 2.0 . . . your kids can play. But WATCH OUT -- you can't see a drowning kid on the bottom of a cloudy pool.

Best wishes,

Ben