Have you put any CYA into the pool? It would have had to be in the form of CYA granules, or using dichlor powder or trichlor pucks to chlorinate. If you haven't added any of that, then shock based on 0 CYA, which is what you have. CYA has to be added in order to be present in your pool water. If you haven't added any CYA, then you need to shock based on a 0 level. Bring your water up to 10 (bringing it up to 12-15 actually wouldn't hurt) by putting the 2 1/2 gallons of bleach in (or 3 1/2 gallons if you want to go up to 15) . Test the water as often as possible and add more bleach to get back up to the 10-15 range as often as possible, as I described in the above thread. If you haven't added any CYA up to now, you can go ahead and add it either via skimmer, where it will sit and dissolve on your filter (but you can't clean your filter until it dissolves, probably 3-4 days) or put it in an old sock and hang it in front of a return to help it dissolve. You want to target around 30-40 ppm of CYA, but only put in about 2/3 of what you think you'll need at first, because it's easier to add more later than it is to add too much and overshoot, requiring higher chlorine levels or drain/refill to compensate.

And as for your other question, I would trust my drop-based test results over any pool store, any time!!!

Janet