pH or EC — which number is actually telling me something?

The short answer

• pH tells you whether the plant can reach what is there.
• EC tells you how much is there.

A plant can starve in a pot full of food if the pH is wrong, and it can burn in a pot with perfect pH if the EC is too high. Reading one and inferring the other is the most common way a diagnosis goes wrong before it starts.

What pH is doing

Nutrients dissolve and stay available across a limited band of acidity, and each element has its own preferences. Drift outside the band and elements that are physically present in the pot become chemically unavailable — the plant shows every sign of running short of something you have been feeding it all along. That is what growers mean by lockout.

The working ranges are not the same for every medium, which is worth knowing because a number that is fine in soil is out of range in coco:

Medium	Working pH range
Soil	about 6.0 – 7.0
Coco	about 5.5 – 6.5
Hydro	about 5.5 – 6.5

Those are the conventional working ranges, and I use them because they are what the field uses — not because I can point you at one study that fixed the endpoints. The claim I can point at is narrower and more useful: above roughly 6.5 at the root zone, iron in particular stops being available, which is why iron problems show up on the newest growth of plants whose pH has drifted up. That one is in the reference text for the field.

So a soil grower reading 7.0 is at the top of their range, not off a cliff. Whether that number matters depends entirely on what the plant is showing you and where.

What EC is doing

EC measures how much dissolved salt is in the water. It is a total, not a breakdown — it cannot tell you which nutrients, only how concentrated the mixture is. That still makes it the number that answers “am I feeding too much or too little,” which pH cannot answer at all.

And it is the one people are least likely to have when they ask for help. A thread will run twenty replies deep debating a pH reading while nobody has established whether the plant is being overfed.

Measure what comes out, not just what goes in

Your input numbers describe your bottle. Your runoff numbers describe your pot.

Those diverge over a run, and the divergence is the signal: salts build up in the medium, and the pH the roots actually sit in drifts away from the pH you poured. If you are only reading the mix going in, you are measuring your own arithmetic rather than your plant’s environment.

Before you trust either number: the meter

This is the part that gets skipped, and it is the reason an otherwise good thread can spend a week arguing about a figure that was never real.

A pH pen drifts. That is not a fault, it is how the electrode works, and it is why they ship with calibration solution. An uncalibrated pen produces a confident-looking number with nothing behind it — and because it looks like data, it outranks the grower’s own eyes in the argument. Calibrate before you diagnose off a reading, and if you cannot calibrate it, say “I don’t know my pH” rather than reporting a number you do not trust. The first is a true statement you can act on. The second sends everyone down the wrong road.

Same discipline for EC: rinse the probe, check it in a known solution, and take the reading at a consistent point in your watering rather than whenever you happen to think of it.

What would show that I have this wrong

If both numbers are in range, stable, and measured on a calibrated meter, and the plant still looks wrong — then this page is not your answer and the cause is somewhere else. Start with where the damage sits and whether it is spreading.

Where my device fits, stated narrowly

Croplock does not measure pH or EC. There is no probe for either in the box and I am not going to imply otherwise — those two numbers are yours, taken by hand, and a fifteen-dollar pen you actually calibrate beats anything I could infer about your root zone from the air.

Sources

• Cannabis in Controlled Environment Production (CRC Press). DOI 10.1201/9781003150442 — iron availability falling away above a root-zone pH of roughly 6.5, and the symptom position that follows from it.
• The per-medium pH bands are the conventional working ranges in general use, given as such. The calibration point is first-party practice, not a citation.

More of these at Answers. The device is at croplock.com.