Hardness basically refers to the measurment of the concentration of dissolved substances before it reaches our taps. This includes metal ions like zinc, calcium, iron, magnesium....ect.
Without the "water-hardness causing substances", the water would have abnormal shifts in pH. These substances buffer any dramatic changes in the pH. Water that is pooly buffered will have more fluctuations in pH as opposed to water that is well buffered.
As a standard rule... hard water is usually basic or alkaline and well buffered, and soft water is usually slightly acidic and pooly buffered.
I'm not sure of many ways of lowering pH without chemicals, maybe someone else can mention some. I know driftwood may help lower pH, however, many kinds of buffers are available at your pet store that will help with your pH problem.