OK. did a bit of checking. Leslie's Power Powder Plus is 65% cal hypo (they also make a stronger 73% cal hypo, Power Powder Pro). You will need to add 11 lbs all at one time to get the FC up to 25 ppm in a 33k gallon pool. Adding a pound at a time won't do anything at all except replace any chlorine burned off by the sun every day since it only adds about 2 ppm FC in a pool your size and 2 ppm FC per day is normal chlorine loss for most pools.

HOWEVER, as I said before, test with an OTO test kit to make sure that you REALLY have a chlorine demand issue (or possible SWCG malfunction) instead of the test just bleaching out and registering low when the chlorine is actually high. OTO does not bleach out, FAS-DPD can overcome bleachout up to about 50 ppm chlorine levels, Syringaldazine which is used in some test strips, also does not bleach out.
DPD, used in many test strips and most pool store testing liquid reagent test kits does bleach out at FC levels from 3 to 10 ppm, depending on how the strip or test kit is forumulated.