Sulfur, pelleted sulfur mixed into the soil with a bit of pelleted dolomite will balance the soil.
Peat Moss can be cut in to lower PH as it has a PH of ~3.5.
Vinegar or citric acid will give a short lived PH down, for me it lasted only minutes.
Water soluble powdered sulfur can work however if you use perlite it can drop to far to fast. The sulfur mixes with water and with time creates sulfuric acid to do the PH down job.