Hi, if the ph is 7, then it isn't ericaceous, because 7 is neutral, and you wouldn't normally add sulphur to pots, only in the garden, and the amount you need varies, depending on whether your soil is sandy, or clay, and the amount of humous in your soil, to change the top 6" of soil from 7 or 7.5 to 6 or 6.5 you need 4 to 8 ounces per square yard, depending on clay, sand or humous content, 4 for sand 8 for clay, so if you want to work it out from there, I would just get some proper ericaceous compost, Derek.

Is 6.5 acidic enough for blueberries Derek? I thought ericaceous compost was nearer 4.5 but having broken my metre I can't check.

Hi Sue, you're quite right, blueberries need a ph of 4 to 5, but dave said the ph was 7, which is why I said it couldn't be ericaceous compost, because as you say, it's more like 4 to 5, I was just giving an example of how much sulphur would be needed, to lower it 1 point.
There is a quick, short term fix, that could be used for pots, which is 2 tablespoons of vinegar to 1 gallon of water, but you can't keep using this method, as it washes out every time you water, which is why I suggested getting some proper ericaceous compost, and repot in that, Derek.

Its astonishing, the number of things you can use vinegar for!

Hi Sue, it certainly is!! :-) Derek.