Runoff pH
The pH of drainage water after irrigation. Runoff pH helps show whether the root zone is drifting outside the range where nutrients remain available.
Runoff pH is the acidity or alkalinity of the drainage water that leaves the growing medium after irrigation. It is used as an indirect check on root zone pH and nutrient availability in container, coco, rockwool, and other soilless systems.
Indoor growers compare runoff pH with the pH of the incoming nutrient solution. A steady upward or downward drift can indicate changes in nutrient uptake, media buffering, alkalinity, microbial activity, or salt accumulation. When pH moves outside the intended range, nutrients can become less available even when EC looks correct.
Common uses:
- Spotting pH drift before deficiency symptoms appear
- Checking whether pH adjustment is holding through the substrate
- Comparing zones that receive the same feed but behave differently
- Confirming whether corrective irrigation is working
Runoff pH is most useful when measured consistently. Collect a representative drainage sample after the substrate is fully irrigated, avoid the first few drops only, and track the trend over time rather than reacting to one unusual value.
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