What is Hardness Plus?

Hi,

Sorry about the dumb question - this pool chemistry thing drives me up the wall. I know it should be simple, but everybody uses different terms.

My neighbor gifted me with a tub of Leslie's Hardness Plus. I'll be damned if I can figure out what it's for. At my local pool store, I was told that my tablets provide acid, and I now have too much acid (and so I took the tablet dispenser out of the pool per their instructions), and the water isn't alkaline enough. They wanted to sell me a tub of something there. I didn't buy it, but don't know what to use in it's place. Oy. Maybe this Hardness Plus is the thing.

Thanks for any help you can provide.