When you add iron sulfate and manganese sulfate and copper sulfate to your high carbonate water, it might also be precipitating them out. Just googled it and says:

Ferrous sulfate (copperas) reacts with calcium carbonate (natural alkalinity) and oxygen to give ferric hydroxide, calcium sulfate, carbon dioxide, and water. FeSO4 7H2O + Ca (HCO3)2 + O2 doubleheadarrow Fe(OH)3 + CaSO4 + CO2 + H2O

I’m shifting my iron, manganese and copper to primarily foliar for these reasons. It may also work to add them in fertigation, as I suggested with the urea.

You could also have a separate reservoir of RO water that you add your urea, iron, manganese and copper to, and you run that in your irrigation once/week. The plants could get enough of those nutrients in one day to last the whole week? That’s a guess. I know John Kempf would say to do all of this in a foliar.