I use rain or RO and made a mix of epsom salts and ag lime. Oyster shell would probably be even better than the ag-lime. 1 part epsom salts (finely ground in coffee grinder) plus 2 parts ag-lime/oyster shell. Make sure it's all powdered and mixed together well. I do 1 tsp per gallon of water, in addition to the lime in my soil. I think a combo of ag-lime/oyster shell mixed with k-mag or sul-po-mag would be even better. No deficiencies.
Do ya'll think that 1tbsp dolemite lime per gallon of soil + black strap molasses at every other feeding until flush will be enough cal/mag to get me through using RO water?