During backwashing, which signal indicates the wash is complete?

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During backwashing, the telltale sign that the wash is complete is when the effluent water becomes clear and the headloss across the filter returns to its normal operating value. This shows the bed has been restored and solids have been flushed away, so flow resistance is back to normal and the filter is ready to resume service. If the effluent remains turbid and headloss keeps rising, the bed hasn’t been fully cleaned yet. No change in turbidity would imply the bed is still dirty or the wash isn’t finishing, and a temperature rise isn’t a reliable indicator of backwashing completion.