Enter the reservoir volume, EC target and price per liter — nutrient liters = V × EC × concentration factor × (1 + waste/100).

Let evaporation compound across the cycle and apply the recycling rate: make-up water = V × (1 + evap × days/100) × (1 − recycling/100).

Build the mix bill: nutrient liters × price, water liters × water cost, plus pH adjustment on the standing volume.

Apply the bulk discount off the mix bill and the 80% recycling recovery credit to get bulk savings and recycling savings.

Add labor as a real undiscounted line, subtract total savings from the mix bill, then divide by volume and days for cost per liter and cost per day.

Read the verdict off savings % (of mix cost) and net cost per liter — green above 20% savings, red under 10% or past $0.25/L.