No idea about the st international soil, but regardless of it having nutrients or not you can any carpeting with just water colum dosing. So, while substrate additives help, they are not mandatory. ADA has a good line, but many people dispute it. I would try it, if you are curious. Personally, I would rather invest on the substrate itself rather than on additives.
A good substrate will definitely help and speed up things. Pay attention to its granularity, should not be too big.
CO2 is a big help. If not available, I would say you should go for Seachem Excel/Glutaraldehyde.
That is the basic idea for most common plants: light (not too much or too little), co2 (or in its absence, at least Glutaraldehyde) and ferts (the whole gang, NPK plus Iron/Traces).
Make sure you keep the water changes in the beggining
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