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Build manual · Deep water culture · Herbs

DWC Basil Tote: 20 L, six plants, and a pump that quietly decides everything

Deep water culture is the most forgiving active system for herbs, and basil is the crop that shows it off. This 20 L tote build runs six plants through seven weeks of continuous cutting. The two things that matter are airstone maintenance and refilling with full-strength nutrient rather than plain water.

By The Grow DeskPublished 20 Aug 2026Difficulty Beginner
System specification45 day cycle
Reservoir
20 Lworking volume
Planting sites
6sites
Pump
8 GPH30 L/h
Air stones
2stones
EC target
1.4 mS/cmtarget
pH window
5.8 - 6.3pH
Light at canopy
320 PPFDat leaf
Photoperiod
16 hper day
Cycle length
45 daysplant to harvest

Top-up routine — Refill to the 15 L mark every 7-9 days with nutrient at full strength, not plain water, because basil strips the reservoir hard.

Bill of materials8 line items
Bill of materials
PartSpecificationQtySubstitute
Storage tote with lid20 L, 40 x 30 x 18 cm, opaque black1Any dark tote; clear ones must be lined with black plastic or algae wins in 4 days
Net pots75 mm rim650 mm pots also work but basil stems thicken and start leaning by week 6
Air pumpSingle outlet, 1.5 W, 1.5 L/min1A dual-outlet 3 W pump run at half flow is quieter and lasts longer
Air stones5 cm round, fine pore2A 20 cm flexible air hose with a weighted end diffuses wider but makes larger bubbles
Silicone airline4 mm ID, 2 m1Standard aquarium tubing; keep it out of direct sun or it goes brittle in one season
Basil seedlings4 weeks old, 8-10 cm, two node pairs6Cuttings root in a net pot of LECA in 9-12 days and crop faster than seed
Two-part nutrientGrow formula, 1.4 mS/cm target500 mL eachA single-part herb blend is simpler but needs weekly agitation or the salts settle
pH and EC pensATC, calibrate weekly1 eachNothing cheaper works here; basil at 1.4 mS/cm punishes a meter that reads 0.2 high
Assembly, in order6 steps

  1. Cut six 75 mm holes with 8 cm of rim clearance

    Mark the lid with a 3 x 2 grid at 12 cm spacing. Leave 8 cm from every hole centre to the tote edge so the lid still carries the weight of six mature plants without sagging into the water.

  2. Run the air line before you fill

    Drill a 6 mm hole in the lid corner for the airline, thread it through, and connect the two stones at opposite ends of the tote. Two stones at opposite corners create a rolling current across the whole 40 cm length; one stone makes a single dead zone where roots go slimy within two weeks.

  3. Charge to 1.4 mS/cm at pH 6.0

    Use 15 L of water, not 20. The empty 5 L of headspace is what stops the lid from pressing down on the solution and keeps the pump from spattering. Basil at 1.4 mS/cm is a well-fed plant; push to 1.8 and leaf margins go crispy while growth rate does not improve.

  4. Set the roots just below the water line

    Unlike Kratky, DWC wants the net pot bases about 2 cm under the surface for the first week so the seedlings never stress. Once new white roots appear in the water, you can let the level fall to 3-4 cm below, since the airstones now supply the oxygen.

  5. Pinch early and often

    At 18-20 cm tall, cut the stem back to the second node. Basil responds by pushing two lateral shoots, and each subsequent pinch doubles the harvest points. Skip this and you get one tall stem that flowers at day 40 and stops producing leaves entirely.

  6. Watch the airstone, not the plant

    Every 10 days, pull the stones and scrub them under hot water. Mineral scale blocks the pores and the flow drops silently, so the water still looks agitated from the top while the bottom goes anoxic. A blocked stone is the most common cause of a sudden mid-cycle collapse in a DWC tote.

Week-by-week maintenanceWeek 1 · Week 2 · Week 3 · Week 4-5 · Week 6 · Week 7

Week 1

EC 1.4 · pH 6.0

  • Water 2 cm over pot bases
  • Check for root emergence by day 6
  • 16 h light

Week 2

EC 1.4 · pH 6.1

  • Lower water to 3 cm below pots
  • First pinch at 18 cm
  • Top up to 15 L mark

Week 3

EC 1.4 · pH 6.0

  • Second pinch
  • Clean airstones
  • Expect 1.5 L per week of transpiration

Week 4-5

EC 1.4 · pH 6.1

  • Harvest 30 % of foliage weekly rather than all at once
  • Top up with full-strength nutrient

Week 6

EC 1.4 · pH 6.2

  • Remove any flower spikes immediately
  • Third pinch to reset the bush

Week 7

EC 1.4 · pH 6.2

  • Full reservoir change: dump, rinse, recharge
  • Inspect roots for brown slime

Airstones are a consumable, not a fixture

The single most common DWC failure is a stone that has slowly scaled up. Water flow looks normal at the surface, so nothing seems wrong, but dissolved oxygen at the bottom of the tote falls and the lower roots start turning translucent and then brown. Cleaning the stones in hot water every ten days and replacing them every three months costs almost nothing and prevents the entire failure class.

Basil drinks more than you expect

A six-plant basil tote at 320 PPFD transpires 1.5-2 L per week by week three and close to 3 L per week by week five. If you top that up with plain water, the reservoir dilutes steadily and by week five the EC is running 0.8 instead of 1.4. The plants do not show an obvious deficiency, they simply slow down and the leaves get thinner. Refilling with full-strength nutrient keeps the EC flat.

Pinching is the yield control

An unpinched basil plant grows a single dominant stem and flowers around day 40, after which leaf production stops for good. Pinching at the second node converts that one stem into two, and the next pinch into four. Three pinches over six weeks takes a plant from a dozen leaves to well over a hundred harvestable ones, all from the same root mass.

When to change the water completely

A DWC reservoir stays usable for about six to eight weeks. After that, root exudates and the salts that the plant did not take up accumulate to the point where EC readings become meaningless: you measure 1.4, but a meaningful fraction of it is sodium and sulfate the basil cannot use. A full dump, rinse and recharge every seven weeks resets the balance.

Tubing diagram: DWC Basil Tote: 20 L, six plants, and a pump that quietly decides everything
Tubing diagram: DWC Basil Tote: 20 L, six plants, and a pump that quietly decides everything

Key points

  • Two airstones at opposite corners beat one big stone every time
  • Refill with full-strength nutrient at 1.4 mS/cm, never plain water
  • Start the water 2 cm over the pot bases, then drop to 3 cm below
  • Pinch at the second node three times for a 4-8x leaf increase
  • Full reservoir change every 7 weeks, stones scrubbed every 10 days

Sources

Please noteNutrient concentrations, pH windows and light figures are general home-system references. Follow your product label, and treat this article as informational rather than professional horticultural advice.

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