# Recirculating deep water culture (RDWC)

> RDWC links several DWC sites to a control bucket and circulates the solution with a pump, so one reservoir sets pH, EC and temperature for every plant and a single chiller cools the lot. It adds circulation and plumbing failure modes to DWC's oxygen and temperature risks. Targets match DWC: 18–22 °C, DO above 6 mg/L, pH 5.6–6.0.

- Canonical: https://genetixbay.com/knowledge/systems/rdwc.html
- Category: Systems · Level: Advanced
- Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Flower · Systems: RDWC
- 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 RDWC reservoir, since bacteria arrive in shared [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) water whatever you do, so you may as well have the good ones. Running sterile is valid only with full commitment: a continuous oxidiser or UV or ozone, clean top-ups and no organics. In RDWC any outbreak reaches every site, so never mix the two approaches.

**What is the difference between [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) and RDWC?** The difference is that RDWC plumbs several DWC sites together and pumps solution through a shared control bucket, while DWC keeps each plant in its own bucket. RDWC gives one place to correct [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md) and temperature, one chiller and more stable chemistry. The cost is plumbing risk: a leak, blocked return or stopped pump, or a [root disease](https://genetixbay.com/knowledge/glossary/root-rot.md), affects every plant.

**How big should the RDWC control bucket be?** An RDWC control bucket is usually about 20–30% of the total system volume, a grower rule of thumb worth verifying for your build. It needs room for the pH and EC probes, the dosing inlet and the top-off. Pair it with return plumbing of at least 25 mm (1 inch) on small systems, because undersized returns overflow the sites.

**How fast should the RDWC pump circulate?** An RDWC pump should turn the total system volume over about 1–4 times per hour, a grower rule of thumb. Circulating too fast adds pump heat to the water, which matters when you are holding 18–22 °C, while circulating too slowly leaves stagnant, warming sites. Circulation does not replace aeration: keep [air stones](https://genetixbay.com/knowledge/glossary/air-stone.md) in every site, not only the control bucket.

**One plant in my RDWC has root rot; what now?** Root rot in one RDWC site means system-wide action, because every site shares the same water and the disease spreads to all of them. Cool the solution to 18–22 °C, keep dissolved oxygen above 6 mg/L, check roots in every site and remove dead root material. Clean and sterilise the whole system between runs to stop the pathogen carrying over.

**Short answer.** RDWC is DWC with the buckets plumbed together and a pump circulating solution through a **control bucket**. You get one place to measure and correct **pH, EC and temperature** and one chiller for every plant, plus larger total volume (more stable chemistry). The cost is plumbing: a split fitting, a blocked return or a stopped pump now affects every plant. Targets are the same as [DWC](https://genetixbay.com/knowledge/systems/dwc.md): **18–22 °C (64–72 °F)**, **DO > 6 mg/L**, **pH 5.6–6.0**.

## How it works

Each site has its own air stones. Solution is pumped from the control bucket into the sites (or the reverse), and returns by gravity through bulkhead fittings near the bottom. Because every site shares water, a root-disease outbreak in one site spreads to all [1].

> **House position: [living reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) 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](https://genetixbay.com/knowledge/glossary/sterile-reservoir.md) 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 | Notes |
|---|---|---|
| Solution temperature | 18–22 °C (64–72 °F) | Chiller sized for pump heat + room |
| DO | ≥ 6 mg/L | Air in every site, not only the control bucket [2] |
| pH / EC | As DWC | |
| Circulation | Turn total volume over ~1–4 times per hour | Too fast heats water; too slow leaves stagnant sites |
| Control bucket | 20–30 % of system volume | Room for probes and top-off |
| Return plumbing | ≥ 25 mm (1 in) for small systems | Undersized returns overflow sites |

## How to run it

1. Level all sites; test with plain water for 24 h and check every joint before plants go in.
2. Probes, dosing inlet and top-off live in the control bucket.
3. Inspect roots in every site weekly; any brown slime means system-wide action.
4. Refresh on schedule; [drain](https://genetixbay.com/knowledge/glossary/runoff.md) via a pump, not by tipping buckets.

## Failure modes

| Problem | Sign | Jardin response [4] |
|---|---|---|
| Split line / leak | One site's level drops while control bucket holds | Per-site level floats flag it; leak pad cuts the pump rail |
| Circulation pump dead | Return flow stops; sites stagnate and warm | "Stagnant bucket" alarm; proof-of-life by current |
| Air failure | DO falls in all sites | Alert, chiller stays on, backup pump if fitted |
| Root rot | Spreads through system | Clean and sterilise between runs; cool water |

## Jardin notes

Jardin method "RDWC": as DWC plus per-bucket level floats, circulation-pump proof-of-life and a stagnant-bucket alarm. Time-to-harm: 2–12 h for air, days for chemistry. Automation level 3 [4].

## Safety

As DWC: GFCI/RCD on every outlet, drip loops, leak trays. RDWC systems hold hundreds of litres; plan for a full spill.

## Common mistakes

- Relying on air only in the control bucket.
- Undersized return lines.
- Mixing plants of different vigour on one system (one EC for all).

## Evidence

Root-disease spread and DO/temperature behaviour in recirculating hydroponics are *Established* [1][2][3]. RDWC-specific design numbers are *Grower practice*.

## Sources

1. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/
2. Cornell CEA, 2016. Leafy greens (GPN): DO and pH guidance. https://cea.cals.cornell.edu/files/2019/06/GPNOctober2016_LeafyGreens.pdf
3. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254
4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins).