PH AND PLANTS...how to adjust and whats right numbers

[The_Rookie]

iv got a walstad starting up and my water from the tap is 6.2 ish..i only had the subersable strips (hate them) iv read that majority of plants i have are in the 6-8 sum being 5.8-7.5 ph ...due to organic substrate im expecting my ph to fall even lower..will oyster shells or crushed coral in filter compartment be enough to help raise? i do have some tuffa rock going in and 2 large honey comb rock(texas holy rock) that is both said to help raise..please let me in on any other secrets in maintaing the proper ph levels.. PS. my house has a purifying system installed for the water