# Deep water culture (DWC)

> In DWC roots hang in an aerated nutrient solution. It grows fast but depends on two things: dissolved oxygen (keep above about 6 mg/L, ideally near saturation) and solution temperature (18–22 °C / 64–72 °F). Warm, poorly aerated water is how Pythium root rot starts. Run pH 5.6–6.0 and EC 0.8–2.0 mS/cm by stage, and treat the air pump as life support.

- Canonical: https://genetixbay.com/knowledge/systems/dwc.html
- Category: Systems · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Flower · Systems: DWC
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Should my reservoir be sterile or full of beneficial microbes?** GenetixBay prefers a [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) for DWC, because bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones. A [sterile reservoir](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md) is a valid choice only if you commit fully, with a continuous oxidiser or UV or ozone, clean top-ups and no organics. Mixing the two, such as routine [peroxide](https://genetixbay.com/knowledge/glossary/hydrogen-peroxide.md) on top of microbes, is what fails.

**What water temperature for DWC?** DWC water temperature should be 18–22 °C (64–72 °F), with 24 °C (75 °F) as the alarm point. Warm water holds less oxygen, about 9 mg/L at 20 °C versus 8 mg/L at 25 °C, and extension research links warm, poorly aerated solution to [Pythium root rot](https://genetixbay.com/knowledge/glossary/pythium.md). In summer, use a [chiller](https://genetixbay.com/knowledge/glossary/chiller.md) or keep the reservoir in a cooler room.

**How much air does a DWC bucket need?** A DWC bucket needs about 1–2 litres per minute of air per 10 litres of solution, a grower rule of thumb, enough to keep dissolved oxygen above 6 mg/L and ideally at 7–9 mg/L. Size the air pump for all buckets plus margin, put air stones on the bottom, and keep a backup pump, because roots suffer within 2–12 hours if the air stops.

**Why are my DWC roots brown and slimy?** Brown, slimy DWC roots with a swampy smell are [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), usually Pythium, which is favoured by warm, low-oxygen solution; tan roots alone can be normal nutrient staining. Respond by cooling the water to 18–22 °C, raising dissolved oxygen, cleaning the system, removing dead roots and using biological root treatments. Wide daily [pH](https://genetixbay.com/knowledge/glossary/ph.md) swings are often an early warning sign.

**How often should I change the DWC reservoir?** Change a DWC reservoir every 7–14 days, or on mass-balance rules if you track what the plants actually take up. Between changes, top off with plain or quarter-strength water as plants drink, and keep checking pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md). If pH swings widely from day to day, inspect the roots for rot before simply buffering and refreshing the solution.

**What pH for DWC cannabis?** DWC cannabis runs best at pH 5.6–6.0, letting the pH drift within that band rather than chasing exactly 5.8. Treat readings below 5.4 or above 6.4 as an alarm. This sits within the accepted hydroponic range of 5.5–6.5. Wide daily pH swings often point to root rot, so inspect the roots before adding more pH adjuster.

**Short answer.** Roots hang in a bucket of nutrient solution kept oxygenated by an air pump and air stones. It is fast and cheap to build, and unforgiving of two things: **low dissolved oxygen (DO)** and **warm water**. Keep solution at **18–22 °C (64–72 °F)** and DO **above ~6 mg/L (ideally 7–9 mg/L, near saturation)** [1][2][4]. Run **pH 5.6–6.0**, **EC 0.6–1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) ([seedling](https://genetixbay.com/knowledge/glossary/seedling.md)) to 1.4–2.0 (flower)**. If the air pump stops, roots are in trouble within **2–12 hours** [5].

## How it works

Roots respire and need oxygen. Water holds little of it, and less as it warms (about 9 mg/L at 20 °C, 8 mg/L at 25 °C at sea level). Bubbles mix the water and keep it near saturation. Warm, low-oxygen solution suppresses roots and favours *Pythium*, which turns roots brown and slimy [1][2]. Leafy-green extension data show growth inhibition below ~4 mg/L DO and failure below ~3 mg/L [3][4]; cannabis-specific thresholds aren't published.

> **House position: living reservoir preferred.** Bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones: GenetixBay prefers a beneficial-microbe reservoir. A sterile reservoir is a valid choice, but only if you commit to it fully (continuous oxidiser or UV/ozone, clean top-ups, no organics) and never mix the two. It's a personal choice; the half-way house is what fails.
See [root rot and Pythium](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md) for both approaches.

## Numbers that matter

| Parameter | Target | Alarm |
|---|---|---|
| Solution temperature | 18–22 °C (64–72 °F) | > 24 °C (75 °F) |
| Dissolved oxygen | ≥ 6 mg/L; 7–9 ideal | < 4 mg/L |
| pH | 5.6–6.0 (let it drift within band) | < 5.4 or > 6.4 |
| EC, seedling/clone | 0.6–1.0 mS/cm | |
| EC, veg | 1.0–1.6 mS/cm | |
| EC, flower | 1.4–2.0 mS/cm | |
| Air | ~1–2 L/min of air per 10 L solution | |
| Gap between net pot and water | 2–5 cm once roots are established | Roots above water get air |
| Reservoir refresh | Every 7–14 days or on mass-balance rules | |

## How to run it

1. Opaque bucket (light causes algae), lid, net pot with [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), air pump sized for all buckets plus margin, air stones on the bottom.
2. Start with the water touching the net pot base; lower it as roots grow.
3. Top off with plain or quarter-strength water as plants drink; full refresh on schedule.
4. Watch roots weekly: white and fuzzy is good, tan from nutrients is normal, brown slime with a swampy smell is root rot.
5. In summer, use a chiller or keep the reservoir in a cooler room.

## Failure modes

| Problem | Sign | Response |
|---|---|---|
| Air pump failure | Wilting within hours, roots dulling | Restart, keep a backup pump; Jardin alerts on zero pump power draw [5] |
| Root rot (*Pythium*) | Brown slimy roots, wilting despite water, smell | Cool the water, raise DO, clean system; biological root treatments; remove dead roots |
| pH swings | Wide daily drift | Check for root rot first; then buffer and refresh |
| Algae | Green film, roots stained | Light-proof everything |

## Jardin notes

Jardin method "DWC": air pump on a monitored plug (power draw = proof of life), chiller plug, level floats, top-off, DO proxy from air-pump power and water temperature. On air failure Jardin escalates alerts, keeps the chiller on, and switches on a second pump if one is plugged into a spare port. Time-to-harm: 2–12 h for air, days for chemistry [5].

## Safety

Water and mains electricity share the space. Use GFCI/RCD-protected outlets, drip loops on every cable and keep pumps above reservoir level where possible.

## Common mistakes

- Warm reservoir in summer.
- One air pump, no backup.
- Adding hydrogen peroxide routinely on top of beneficial microbes (they cancel).
- Chasing pH 5.8 exactly instead of letting it drift within band.

## Evidence

Temperature and DO effects on hydroponic root disease are *Established* in extension literature for other crops [1][2][3][4]. The hydro pH band (5.5–6.5, with drift inside it normal) is accepted practice from extension and grower consensus; cannabis-specific DO and temperature targets are *Grower practice*.

## Sources

1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (68–72 °F). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/
2. e-GRO Alert (Cornell / collaborators). Pythium root rot on hydroponically grown basil and spinach (cool solution 68–72 °F; DO near 8 ppm). https://www.hortidaily.com/article/6040777/pythium-root-rot-on-hydroponically-grown-basil-and-spinach
3. Cornell CEA. Hydroponic lettuce handbook (dissolved oxygen; stress below ~4 mg/L). https://cea.cals.cornell.edu/
4. Cornell CEA, 2016. Leafy greens (GPN): DO ~7–8 ppm, failure below 3 ppm. https://cea.cals.cornell.edu/files/2019/06/GPNOctober2016_LeafyGreens.pdf
5. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins).