Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur. These can be found at a garden supply center. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil. Sulfur, however, requires some time for the conversion to sulfuric acid with the aid of soil bacteria. The conversion rate of the sulfur is dependent on the fineness of the sulfur, the amount of soil moisture, soil temperature and the presence of the bacteria. Depending on these factors, the conversion rate of sulfur may be very slow and take several months if the conditions are not ideal. For this reason, most people use the aluminum sulfate.

Do a google seach to be able to calculate the application rates correctly.
greenman:D Reviewed by greenman:D on . PH Lockout ? Here are a couple of pics. My friend has been taking care of them for a few weeks and this is what happened. They are in FFOF with about 40% perlite. I flushed them with 5 gallons each of 7.0 ph plain (tap unfortunately) water tonight and the runoff was between 7.3 and 7.5. They have been getting half doses of Thrive alive, Grow Big, and Liquid Karma at 2/3 of their waterings (the other waterings are plain water). The first two pics are Sour Diesel and the others are blueberry and they are Rating: 5