Sandy,

Remember the two things that consume Cl...the Sun and "bugs".

With your low CYA reading, I'll bet the Sun got some of that Cl.

Put that Cal Hypo in at dusk and you'll get much more effective use out of it....hide it from the Sun.

As an aside, ask the pool store for a 25 or 50 lb tub of Cal Hypo. You'll save a lot of bucks and I believe you'll use it all this Summer. (you still need to get your calcium up and it will take quite a bit) If you cap it tightly it'll be good next year if you don't use it all.