Lowering PH level for potted roses?

The soil in my potted roses was off the chart on my ph meter (which only goes to 8). I know the meter works because I tested it with apple cider vinegar (the only thing I had at the time). I've tested the soil according to the directions on the meter, and every which way besides.

I currently have 4 roses planted and another still in it's "body bag", 3 seem to be doing fine, but I had several that didn't make it and one of the newer ones I just planted is starting to look like the ones that didn't.

The soil is all the same brand of potting soil, and since it was new I didn't think it needed to be tested & so I didn't until I purchased the meter and needed to see if it worked.

I'm afraid to try to mix in sulfur since it may disturb the roots. Is there anything I can sprinkle or pour onto the soil that may help my dying rose?

(The rose that's dying had green branches when I bought it, but over the last 2-3 weeks the branches have turned black, and the new red/pink branch-buds turned brown and dried up, it was labeled as a "blue bubble" rose)

The ones that are surviving are a pink fairy, black beauty, and what was labeled as a blue boy (though this one came from one of the lower quality suppliers)