lol you dont want "synthetic nutrients", but are willing to buy floragro if you have to?
they are exactly the same thing.
there IS an alternative, however the upfront cost is usually to much for folks to bear.
you need quantites of fertilizer salts and a decent scale able to do +- a tenth of a gram, and 250+ grams.
i started out buying like 60 bucks worth of ferts from some aquarium place... i ranout after a year or so and then bought like 200 bucks worth of calcium nitrate, potassium nitrate and monopotassium nitrate and peters STEM.
this was back in like 2013, and it should last me several more years at the rate im using it.
i dont bother buying epsom salts online. i buy a few lbs at a time at the CVS down the street. there is no sense in storing 10's of lbs of epsom salt because its readily available.
that 200 bucks i spent was probably like 2,000 dollars worth of flora grow, micro and bloom.
honestly though. i find myself reccomending the premixed salt formulations like maxigrow more than i do DIY salt formulations.
id only reccomend doing what i do, if you are looking to tinker with formulations or produce different formulations for different plants.
also... you can get somethign like maxigro and just add more calcium nitrate or phosphate or what ever you want to further fine tune, but this requires a bit of math that may or may not easy for you depending on your math history.