are reliable if used correctly, you have to follow the testing instructions to the letter. These tests are simple, inexpensive ways to ensure that your garden has the best foundation possible. Once you've ascertained whether your soil Ph is problematic or not, you can work on solving the problem.
To raise or lower the pH level in the soil either Limestone or Sulfur is utilized. There are other materials that will do the job also, but the aforementioned are the most widely used. Sulfur reacts with bacteria in the soil and produces sulfuric acid, which releases hydrogen ions thus causing the soil to become more acidic and the pH level is lowered. See: Tracking and Adjusting Soil pH
To reduce the soil pH by 1.0 point, which raises the acidity. Mix in 1.2 oz of Garden Sulfur per square yard.
If the soil is sandy Mix in 3.6 oz per square yard.
Add the sulfur into the upper 1/2 foot of the soil in the area where you will be planting the blueberry bushes, or work it in on existing plants being sure not to damage the root system.
In the rare instances when you’ve done all the tests, and taken the necessary steps to correct the problem, and still your blueberries aren't doing well, you probably have a mineral deficiency See - Nutrient Disorders in Vegetable Gardens. At this point I would suggest contacting your local cooperative extension service. They will advise you on collecting soil samples and sending it to them for analysis. They generally return a report that should alert you to any mineral deficiencies and the steps to correct those issues.
Organic amendments such as pine needles will gradually lower soil pH, but this takes several years, Some organic fertilizers such as cottonseed meal will do the same. The addition of sulfur will lower pH more quickly, but it can also take a little time, there is no magic pill, to instantly fix the pH.
Once your blueberries are established, mulching with pine needles and or shredded pine bark will help maintain an acidic soil which is essential for Blueberries. Coffee grinds and spent tea leaves will also help maintain the Ph - over time. As will human urine -See: Urine as a Fertilizer
Some tap water contains dissolved lime, which will lower the soil pH , while you are trying to raise it. If you believe this is an issue adding a modest amount of vinegar, say about a teaspoon per gallon of water should resolve this.
Another route, if you don't have the time or inclination to maintain the soil as need be, is to try growing shadbush which produces the Serviceberries that is very similar to blueberries in taste and appearance. It is easier to grow and doesn't have the rigid requirements that blueberries do. They are tolerant of a much wider range of soil.