Should You Top Off DWC With Plain Water or Nutrients?

Why

A top-off has two jobs: replacing water and restoring nutrient concentration. Either method can work if the reservoir ends at the correct volume, EC, and pH. In standalone DWC, a nutrient-solution top-off can work. In RDWC, every site shares the same solution, so I separate the adjustments.

I record EC to preserve the trend, restore the level with pH-adjusted RO water, then circulate the loop. If EC is low, I add supermix gradually through the control reservoir, circulate, and recheck EC. My supermix is one gallon of RO water with stage-appropriate nutrient ratios. Each component goes into the water in order, never combining raw concentrates. Once mixed, I adjust its pH. After the adjustments, I verify the final system pH, the reading that counts.

A nutrient top-off works too, but its strength must account for the missing volume and the reservoir’s current EC. I use water first in RDWC because it restores a consistent volume and lets me correct one variable at a time.

Neither method replaces regular reservoir changes. EC measures total concentration, not the balance of individual nutrients. Science defines the destination. Your system determines the route.