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nutrients that i and also GPSFrontier had mention do not come from a hardware store.they are developed and used by professionals that i know for fact have been in the business since the 70's.
i believe the pros would be using Gh if that was cost effective.
My tomatoes last summer got severe Hail damage so i kind of gave up on them and they just received water only without any nutrients at all for two months. i was surprised how well they did without me hardy paying any attention to them.
the lesson i learned is don't give up on my plants because they are tough survivors. [The Hail hit them really hard]. But also I do not feel that i have to be so obsessed with the nutrients i give them.