I have planted three pots of blueberries in 22" pots about 3 feet apart in my backyard for about a month. I have purchased those commercial pH meter (ones you can get from Canadian Tire or Home Depot) and the pH level seems to be slowly dropping from about 6.5 from the beginning to 7 now. I initially used tap water, but not that much since it has been raining a lot in Vancouver this month. Furthermore, I have just got myself a rain barrel so it can enjoy a bit more acidic rainwater soon. Nonetheless, the pH level of the soil still concerns me. While those cheap pH meter may not be very accurate, still 2 of the 3 blueberry bushes didn't seem to grow. The leaves are not yellow yet, but it does seem to pale a bit. The soil in the pots are regular potting mix and peat moss, mixed in 1:1 ratio. While some sources says peat moss should be acidic enough, it didn't seem to be the case for me (at least that's what the meter says). I read that applying ammonium sulphate does the trick in the short term, while spraying elemental sulfur works nicely in the long term. However, I am having difficulty finding these either online or at local large garden stores. In fact, the stores often suggest the use of aluminum sulfate, which I do use for Hydrangeas, but I read from many places that it is toxic to blueberries (despite the package says it is great for BB?!) So any advice to acidify my soil for the BB? And where can I get them?