How to create lower pH soil for blueberries in a large container

I have 4 very large plastic containers (about 65 gallon) that I want to grow blueberries in, but the pH of my natural soil is too high (6.5 to 6.8).

Is there a mineral that I can add for long term soil adjustments to about 5.0 pH?  If I can do this once and just add compost yearly that would be great.

I am thinking couple of cups of ag sulfur and 30% peat mixed with 70% local soil.
I think a hole on the side of the containers would keep them from flooding so maybe a couple 1/4 inch holes 1/3rd the way up from the bottom.

Does this make sense? any suggestions?

I have mine in 100% peat moss. I top dress it with a mushroom compost from a local grower because its advertised as " slightly acidic". They are doing well and looks like i will have success. They were planted last year and they are leafing out right now.

My failure in the past (at least i think the failure was) had been watering with alkaline well water. I now have decent storage of rainwater which got me over the hump.

Oh, i did add some seawater into the peatmoss. My thought was it would help with minerals since i had no "soil" in there.