I acidify my water with pH Down from the hydroponics store. To lower the pH from 8 to 6.5, it takes me 2-3 cups for my 175 gallon pond. I tried vinegar, but with regular vinegar I had to add almost a whole gallon for 175 gallons. Then I tried horticultural vinegar, and it takes about the same amount as the pH Down, only here at least, the pH Down is cheaper, so I have stayed with that.
I also use a quick acting sulphur that I top dress with every so often. It is Espoma Organic Soil Acidifier that I get at Home Depot, and has dosages for pots, which I really like.
Then, when I pot my baby Miracle Berry bushes up, I use a fast-draining soil mix that uses peat moss and not coco coir, since coco coir can have a higher pH than peat moss.
So far, mine are doing awesome, and I get so many fruits that I can't give them away fast enough. Once people have experienced the "party trick", then the novelty is gone and they don't usually want more. So I just eat them by the handful while working in my greenhouse.
Cheers,
Carolyn