I have this stuff:
https://www.espoma.com/product/soil-acidifier/
The instructions says 1T per 4" diameter. I'd have to add 3T since the 5 gal buckets are about 12" across, then dig that into the top soil and water it.. but I don't want to water as I think that flushed the organic fertilizer ring and caused this in the first place. So.. if it just scratched in, will it slowly reduce the pH of the soil, similar to how the fertilizer gets slowly absorbed over time through wicking?
Remember, I am doing a variation of sub irrigated watering, using buckets sat atop gutters.
Or maybe I dissolvesome into the gutter and let the plants wick it up? Not sure how much though, hmmm.
I kind of feel like I shouldn't do this. Maybe I'll test with one of the buckets where I have a tomato duplicate.