A new system looks clean: the plastic shines, the tubing is clear, the reservoir is empty. Manufacturing lubricant, plasticizers, packaging dust and glue residue from the fittings are already inside it. Fill it with nutrients straight away and for the first week the plant takes up a mixture of your recipe and whatever the factory left behind.
Quick glossary: Priming is the preparation of a new or idle system before start-up: flushing, disinfection and verification of every component before a plant goes anywhere near it. Disinfection is treating surfaces and tubing with a solution that kills pathogens and breaks down biofilm. Biofilm is a colony of microorganisms attached to surfaces inside the system, acting as a pathogen reservoir. Contact time is how long the disinfectant must stay on the surface for the full effect.
Why a New System Needs Preparation
Plastic, silicone and PVC fitting cement release chemical residues in the first days after assembly. None of it is toxic to people, and for the root it is stress plus an extra chemical load that pushes pH and EC in an unpredictable direction.
Beyond that, any system collects dust, airborne microorganisms and traces from your hands during assembly, a new one included. Start it up unprepared and those microorganisms get an ideal environment of nutrient solution and warmth, so biofilm begins forming before a single root reaches the tray.
Priming belongs in the category of conditions, rather than nice-to-haves. It is what makes the first two weeks of growing predictable.
Step 1 - Flushing: Wash Out the Factory
Fill the system with clean water, no fertilizer, and run circulation for 30-60 minutes. Drain. Repeat twice. The target is the plasticizers, the dust and the assembly chemistry.
Check pH and EC of the drained water after the first flush. An EC above 0.3 mS/cm, or a pH far from that of the incoming water, means there is still something to wash out. Keep flushing until the drain readings stabilize.
Watch the dead zones, the places where water sits instead of circulating: corners, horizontal branches, the low points of tubing runs. Where the flush water does not reach, the residue stays.
Step 2 - Disinfection: Kill What Is Already There
After flushing, fill the system with a disinfectant solution - hydrogen peroxide, sodium hypochlorite, or a quaternary ammonium compound, depending on what comes next. Each option has its own contact time and its own rinsing requirements before plants go in.
- Hydrogen peroxide (H₂O₂, 3-5%) breaks down into water and oxygen, leaves no residue and is safe ahead of start-up. Contact time: 30-60 minutes with circulation running.
- Sodium hypochlorite (chlorine bleach, 50-100 ppm active chlorine) is effective and cheap, and it demands thorough rinsing afterward, because residual chlorine suppresses the root and the beneficial microorganisms alike.
- Quaternary ammonium compounds (QAC) work well against biofilm and must be removed completely before a living system is started.
When the contact time is up, drain the disinfectant and flush the system with clean water at least twice. Check drain EC and pH: if the drained water still reads higher than the clean incoming water, the disinfectant is not fully out and the flushing continues.
Step 3 - Testing the Hardware Under Load
With flushing and disinfection done, fill the system with working solution and run it in normal mode for at least 24 hours before planting. This is diagnostics rather than a warm-up.
What that day has to show you:
- Pump: steady flow without pulsing, no air locks in the tubing
- Timers and valves: firing at the calculated times, full drain or ebb completing within the intended window
- Reservoir pH and EC: stable 12 hours after adjustment; pH creeping with no cause means a chemical reaction with the system materials
- Liquid level: no unnoticed leaks, reservoir level matching the calculation
Hardware problems are better found now, before a plant is standing in the tray and every hour of downtime is a loss. More on choosing and setting up equipment.
Three Mistakes That Cost the Most
Skipping the flush because the plastic is new and clean. New plastic releases more residue than plastic that has already run several cycles. The first flush always puts EC and pH somewhere other than you expect; skip the check and that surprise waits for you with the plant already inside.
Not holding the disinfectant contact time. Fill and drain is not disinfection. Most products need at least 30 minutes of circulation to reach every surface, the dead zones and the inner tubing walls included.
Planting straight after disinfection with no test run on working solution. A hardware fault found during priming is a minor complication. The same fault found on day three after planting is plant stress and lost time.
How to Tell the System Is Ready
After priming: EC and pH of the working solution hold for 12 hours with no corrections, the pump and timers have completed at least two full cycles without a fault, there are no leaks, and drain EC after flushing matches the EC of the incoming water.
If you want to go deeper: Sanitation and biofilms: keeping the system clean between cycles is the next logical step after the first run, once the system is working and the question becomes how to keep it that way.