Although hardness and pH are related they are different things. Driftwood will lower pH because it releases acidic tannins, but it wont remove the dissolved minerals that are 'hardness'
There is no simple way ( something in a bottle ) that will remove hardness. The simple way is to use soft water ( water from a RO filter or rainwater) and dilute your hard water with that.
The real question is whats your hardness now, and what fish do you want to keep. Many fish will happily adjust to water thats a bit out of their natural range as long as things are stable.
Cheers
Ian