Sorry about the Costco purchase; that's why I tell people to by pool chems at Sams, not Costco. Sams sells (at least for the last 3 years) undiluted trichlor and dichlor; Costco sells the mess you've got. I don't remember what ELSE is in it, so I can't recommend it at the moment, but it's probably OK so long as there is NO copper in it.

+ You can test for CYA at any time; chlorine levels don't affect the test.

+ Volume calculation: 7.48 gal/ft3 x [(3.5 x 9 x 24) + (6.5 x 14 x 13) - (14 x 0.5 x 3 x 3)] = ~14,000 OR 11,900 gallons.

spreadsheet here: http://goo.gl/wE4tN -- the difference is whether 3.5' is the WATER depth, or the POOL depth.

+ bleach is just a predictable way to add chlorine, that we can recommend without worrying about side-effects or what ELSE is in the bleach. Algae doesn't care whether you have FC = 30 ppm from bleach or Shock Plus. *YOU* may care if the Shock Plus has enough copper to turn hair green and stain your pool!