Sulfer burners have been in use for years... they work.
Anything that changes the PH I have heard milk, baking soda' ect
I had some Citro-fresh made from orange peel and aloe that slowed growth quite well sold in Pirth.
But the best is that Advance Nutrients Purranah (and I think AN is bullshit)
beneficial fungi, it works by using up the food with fingi that does not harm the plant... that shits amazing... there is probably cheaper stuff on the commercial market today...
FC