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

By Curtis Olson — retired software developer, home grower, and the builder of the device this site is about. More about me and why I built it. · Last reviewed 2026-10-27

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.

IG-030Two numbers, two questions

pHECAnswersCan the plant reach what is there?How much is there?Fails asLockout — starving in a pot full of foodBurn, or hunger — too much or too little saltBottle vs potWhat you poured drifts from what the roots sit inSalts build in the medium; read the runoffThe meterA glass electrode that drifts: calibrate before you diagnoseRinse the probe, check it in a known solution, read at a consistent pointCannot beA two-prong soil stick — no electrode, no buffer, no calibrationThe stick's 'fertility' needle — an arbitrary scale, no unit

Iron falls away above a root-zone pH of roughly 6.5 (the reference text); the per-medium bands and the calibration point are working practice, as the page says.

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.

Do I even need to check pH?

It depends on what the roots are in, and the honest answer for a lot of soil growers is “less often than the internet says.”

In soil, the medium does much of the work. A peat or compost-based potting mix is buffered: it resists a change in pH, so water that goes in a little high or low gets pulled back toward the mix’s own level. That is why plenty of soil growers feed plain or lightly fed water, never adjust, and grow fine. It is not that pH stops mattering; it is that the soil is holding it for them. The buffer is not unlimited. Hard, alkaline tap water poured in for months can wear it down, and a soil grower should start reading the runoff when the first signs show on the newest growth (the iron point above), not before.

In coco and hydro, there is no such cushion. Coco holds very little buffering capacity and water culture holds none, so whatever pH you pour is close to what the roots sit in. That is why coco and hydro growers check every feed, and why “I never check and I’m fine” advice from a soil grower does not carry over.

So: in soil, check when something looks wrong or your water is hard; in coco or hydro, check every time. Either way, a reading you can’t trust is worse than none, which is the next part.

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.

How do I know my pH pen is right after calibrating?

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.

Calibrating does not prove the calibration worked; checking does. After you calibrate, rinse the pen and put it in a fresh buffer it was not just set to: if you calibrated at 7 and 4, read a fresh pour of the 7 again, or a 10 if you have one. A pen that lands within about a tenth on a buffer it has not just been adjusted to is telling you the truth. One that wanders, takes minutes to settle, or will not hold the second point is worn, and electrodes do wear out. Use buffer that has not been poured back into the bottle, because a used buffer has been diluted by whatever was on the probe. And if you own two pens that disagree, neither of them settles it; the buffer does. That is the whole method, and it costs a sachet of solution.

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.

A two-prong soil stick — the “soil meter” — is not a pH meter. The “3-in-1” and “6-in-1” garden probes read a small voltage between two metals pushed into damp soil. There is no glass electrode, no buffer solution and no way to calibrate one, so the number it shows cannot be checked against anything — which is the one property a diagnostic reading has to have. A soil reading of 7.5 off a stick, in living soil that is feeding a green plant, is a reason to test properly, not a reason to amend. If you grow in soil and want the number, take a slurry or the runoff and read it with the pen you calibrated; if you grow in coco or hydro, the runoff is the number and the stick has nothing to add.

And the “fertility” needle on the same stick is the least useful of the three. It has no calibration path either, it reports an arbitrary low-to-high scale rather than a unit you can compare with anyone, and what it responds to is bound up with how wet the medium is and how corroded the prongs are. The practical problem is not that it is vague — it is that a comfortable reading is taken as evidence there is no salt problem. If a plant has stalled and you want to know what is in the root zone, the runoff reading above is the measurement; “the meter says the fertilizer level is good” is not.

If the pH of what goes in keeps climbing, look at the order you mixed it in. Silica supplements are potassium silicate, and potassium silicate solutions are strongly alkaline — that is chemistry, not a brand quirk. Added last, or straight after a calcium-carrying concentrate, it raises the pH sharply and can drop out with the calcium as a haze. The usual working order is silica into the water first and fully mixed, then base nutrients, then anything calcium-heavy, then adjust the pH at the end. A reservoir that reads fine the day you mix it and high the next morning is telling you the same thing: something alkaline is still coming out of solution, and the fix is the order, not more acid.

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.
• That potassium silicate solutions are strongly alkaline, and that silicate is added to the water before calcium-carrying concentrates, is general solution chemistry as set out in hydroponic nutrient-formulation references; the mixing order is given as the usual working practice. The point about two-prong soil sticks is first-party practice: they cannot be calibrated, so their reading cannot be checked.

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

Also read: Is it cal-mag? · Is my pale new growth a deficiency? · Is this the fade, or a deficiency? · Is it wind burn or nutrient burn?