Just saw your first post -- with a 1600 gallon pool do NOT get a bottle of dichlor, like the Kem-Tek. The bagged dichlor from Sams is a MUCH better idea, since it will keep much better.

On a 1600 gallon pool, a single 1lb bag of dichlor will add ~40 ppm chlorine and ~37 ppm of stabilizer. HOWEVER, with a 1600 gallon pool, you need to drain & refill every 2 weeks or so, if you are using it regularly. The dichlor will work very well with that.

If you can't buy it at Sams, here's another option at Amazon:
Nava Chemicals Quick Dissolving Chlorine Shock, Pack of 6 1-Pound Bags
Please note that, when I checked just now, NONE of the other bagged shock products on Amazon were undiluted dichlor!