The One Feeding Chart: EC by Stage for Small DWC — Replacing Our Three Old Ones

A feeding chart only works if there is exactly one of it. For most of this season, ColaXpress had four — three blog posts and a /grow/ reference page, each carrying its own EC-by-stage targets, none agreeing with the others. A grower who read two of our pages back to back could reasonably conclude that we did not know what a flowering plant should eat. That was a fair conclusion. This page is the fix.

Below is the one canonical EC-by-stage table for a small deep water culture (DWC) cannabis grow — a single bucket or a compact cabinet reservoir. Every other feeding number on this site now defers to it. Farther down is the part most sites skip: exactly what our old charts said, why they disagreed, and what happened to each one.

The canonical chart: DWC EC levels by stage

These are total-solution targets: what your meter reads in the finished, circulated reservoir, starting water included. EC is in millisiemens per centimeter (mS/cm), the unit most meters simply call EC. The ppm column is the 500 scale only — the scale problem gets its own section below.

These are working ranges, not set points. Enter each stage at the low end and let the reservoir trend tell you whether to climb. The asymmetry is the reason: in a small reservoir, raising EC takes a minute, while pulling salt back out means diluting or dumping the mix. The late-flower taper is deliberate too — demand falls as the plant finishes, and holding peak strength into ripening mostly builds salt, not bud.

If you are new to the system itself, start with what DWC is and how the root zone works. This chart assumes the bucket is already running.

pH runs on its own canon: keep the band at 5.5–6.2 with a target of 5.8–6.0, treat 5.5 and 6.5 as hard limits, and remember that drift inside the band is normal, not an emergency. The full DWC nutrient schedule pairs this table with pH targets and NPK emphasis for every stage.

Notice what the flowering row does not do: it never reaches the 2.2–2.4 mS/cm peaks printed on some feed charts. That is on purpose, and the reasoning is laid out in the disagreement section below.

EC first, 500-scale ppm second, never bare ppm

An EC of 2.0 mS/cm reads 1000 ppm on a meter using the 500 (NaCl) conversion — Hanna and most US meters — but 1400 ppm on a meter using the 700 (KCl) conversion, such as the Bluelab Truncheon. Same solution, two numbers 40% apart.

That is why a bare ppm figure is meaningless. If a chart, a forum post, or a bottle label gives you ppm without naming the scale, you cannot use the number safely. ColaXpress publishes EC first and 500-scale ppm second, and never an unlabeled ppm figure. If your meter only displays ppm, find out which scale it uses before you trust any chart — including this one.

Our old charts disagreed. Here is the correction.

NO MYSTERY is the rule this site runs on, and it cuts both ways: if we expect you to measure your reservoir, you get to measure us. This is what the site was telling you before today, chart by chart, oldest first:

• Best Nutrients for DWC Cannabis (August 3): seedling 0.3–0.6, early veg 0.6–0.9, stretch and early flower 0.9–1.3, mid flower 1.2–1.6, late flower 0.8–1.3. The most conservative of the four.
• How to Mix DWC Nutrients (August 9): young plants 0.4–0.7, veg 0.8–1.2, flower 1.2–1.8.
• Hydroponic Nutrient Mixing Guide for Small Grows (August 15): young plants 0.4–0.8, veg 0.8–1.4, flower 1.4–2.0. The most aggressive of the blog charts.
• The /grow/ DWC nutrient schedule: seedling 0.4–0.8, early veg 0.8–1.3, mid-to-late veg 1.3–1.8, early flower 1.8–2.3, late flower 1.6–2.0, plus a 0.0–0.4 flush. Its early-flower peak exceeded anything the blog ever recommended.

Compare the flowering rows. Depending on which of our pages you landed on, peak flower was 1.2–1.6, 1.2–1.8, 1.4–2.0, or 1.8–2.3 mS/cm. The top of the /grow/ range was nearly double the bottom of the oldest blog range — on the same site, for the same bucket.

How it happened is ordinary, which is exactly why it is worth saying plainly: each page was written on its own, checked against a different source chart, and never measured against the pages we had already published. No single chart was reckless — each sits inside the spread that credible sources publish — but a site whose premise is that nothing in the cabinet should be a mystery number cannot leave four answers to one question standing.

The fix, page by page. The August 15 mixing guide now redirects here; its chart was the closest to canon, but two mixing guides was one too many. How to Mix DWC Nutrients stays live as the mixing procedure — order of additions, aeration, meter habits — with its numbers corrected to the table above. Best Nutrients for DWC Cannabis stays live as the guide to choosing a nutrient line, with its stage table corrected the same way. The /grow/ schedule keeps its job as the full reference, now matching canon, including retiring that 2.3 peak. From today, stage numbers live in this one table, and the procedure and product pages link to it instead of restating it, so any future correction happens in a single place.

Why honest sources disagree — and why the canon is moderate

Credible published targets for peak flowering EC run from roughly 1.6 to 2.4 mS/cm, depending on cultivar, system, and irrigation style. That spread is not sloppiness; it is real variation. A heavy-feeding cultivar under strong light in drain-to-waste coco genuinely tolerates more than a modest plant in a bucket.

Two things pull the DWC answer toward the lower middle of that spread. The first is the system: DWC roots sit in aerated solution around the clock, with continuous access to water and nutrients and no dry-back between irrigation events, so the solution does not need to be as concentrated as a feed that must carry a pot through hours of drying. DWC typically runs lower EC than drip or drain-to-waste setups for exactly that reason. The second is the research on pushing higher: in controlled work from Bruce Bugbee’s lab at Utah State, doubling solution strength from 2 to 4 mS/cm produced no gain in yield or cannabinoids. The plants took up more minerals without making more flower — the pattern Saloner and Bernstein documented as luxury uptake. Past the point of sufficiency, raising EC adds burn and lockout risk without adding yield.

We hold this chart with moderate confidence — a defensible center for small DWC, not a law. If your cultivar and two runs of notes argue for 2.2 mS/cm in mid-bulk and the leaves stay clean, your notes win. What the table protects you from is starting at 2.3 because one chart said so.

Know your starting water before you feed

The table describes the finished solution — starting water included — so the first number you need is the one nobody can publish for you. Before the first feed of a run, measure the water by itself: fill the reservoir, let it reach room temperature, and read the EC with nothing added. Write it at the top of your log; that number is your baseline.

We are not going to print a typical tap-water number, because there is no such thing. Source water varies city to city, block to block, and season to season. The only baseline that matters is yours, and it costs thirty seconds with the meter you already own.

What the baseline changes is your room to feed. The working rule: subtract your baseline from the top of the stage range, and that difference is your actual nutrient budget. Soft water or reverse osmosis reads near 0.0 mS/cm, so the entire range is available for nutrients — though very clean water may need calcium and magnesium, per your nutrient line’s directions. Hard water spends part of the budget before you open a bottle: a 0.4 baseline against an early-veg target of 0.8–1.2 leaves only 0.4–0.8 for actual nutrients. And not everything in hard water is food — bicarbonates raise the baseline and push pH upward without feeding the plant at all. If your baseline swallows a third of the seedling target on its own, blending in RO water is a cheaper fix than fighting the meter all run.

How to read the trend

A single EC reading tells you concentration. Two readings a day apart tell you what the plant is doing with it. Track water level and EC together, at the same time each day:

• Level falls, EC rises: the plant is drinking water faster than it takes nutrients. The solution is too strong. Top off with plain pH-adjusted water and mix the next reservoir lower.
• Level falls, EC holds: balanced uptake. The strength is right for this stage. Change nothing.
• Level falls, EC falls: the plant is consuming nutrients faster than water. It can likely handle more — raise the next mix modestly, about 0.2 mS/cm at a time, staying inside the stage range.
• Neither moves much: the plant is not working. Do not feed a stalled plant; check root condition, reservoir temperature, and pH first.
• EC looks fine but the plant does not: if pH has pinned against 5.5 or 6.5, or climbs daily no matter what you correct, nutrients can be locked out of reach at any concentration. Deficiency-looking leaves over a full reservoir are the classic sign — compare against the signs of nutrient lockout before adding anything.

Three of those five situations end with you adding nothing, and that is normal. The discipline is in the increments: chasing a hungry plant up the scale in big jumps ends with burnt tips, and raising EC does nothing for a plant that has stopped drinking — that problem lives in the roots, the temperature, or the pH.

What the chart assumes

These ranges assume the rest of the reservoir is inside its own canon. pH sits in the 5.5–6.2 band with 5.8–6.0 as the target. Reservoir temperature holds near 65–70 °F — fully aerated water carries only about 8.3 mg/L of dissolved oxygen at 77 °F (25 °C), that ceiling falls as the water warms, and roots slide into stress below roughly 5 mg/L. And the air pump and stone keep the water at that dissolved-oxygen ceiling around the clock. A warm, under-aerated reservoir will make any feed chart look wrong, because the roots cannot use what the water is carrying.

Who this chart is for

This table is built for small DWC cannabis grows: one to a few plants, single buckets or a compact cabinet reservoir, home light levels, photoperiod or autoflower cultivars of ordinary appetite. If you run large plants in drain-to-waste coco under commercial light, your numbers will land higher and this is not your chart. Even inside small DWC, cultivars differ enough that the table is a starting point and your own logged trend outranks it.

One chart, measured against itself, beats four charts that each looked right alone.