Dry Acid, aka Sodium Bisulphate, or aka Monosodium Hydrosulphate
This chemical is something of an “organic gardening unknown” as it is generally only used to lower pH in swimming pools and spas, cleaning steel in steel manufacturing/ processing and several other industrial processes. Let me say right now that this chemical, in its aqueous diluted form, can not only act as a strong herbicide, but it also works as an innocuous cleaning “antimicrobial” agent with livestock, cutting down on Campylobacter and Salmonella bacteria found commonly in faecal matter. This means that your livestock will also be healthier!
Dry acid can also be used to lower soil pH in the event of over fertilisation making it harder for the plant to uptake nutrients which may be in over supply at the higher end of the pH scale (Alkaline Salts).