Are you SURE you don't have mash pH issues? How do you know?
If you just need to boost something like S04, yes, you can add that to the boil.
I take ph readings on every batch.
I've been blessed with pretty good water for brewing direct from my well.
From Dunkels to Pils it reads at 5.2 to 5.4 in the mash
Sodium................................ 14
Potassium............................. <1
Calcium...................................14
Magnesium...............................3
Total Hardness CaCO3...............48
Nitrate......................................1.0
Sulfate.......................................4
Chloride....................................15
Carbonate..................................<1
Bicarbonate HCO3......................37
Total Alkalinity CaCO3................31
Flouride......................................0.03
Total Iron....................................<0.01
TDS ..........................................110
pH..............................................6.7
