Overview
Algae and bioslime build up inside greenhouse irrigation lines, and it rarely shows until an emitter clogs or watering goes uneven across the bench. That layer shelters bacteria, consumes nutrients out of the feed water, and narrows the bore until flow drops.
Chlorine dioxide penetrates the protective slime layer and reaches the microbes underneath it. Selective Micro Technologies ran three trials with Selectrocide® on fouled irrigation tubing: an overnight shock, a continuous low dose held for 22 days, and a section of heavily fouled tubing pulled out of a working greenhouse.
Objectives of Testing
The trials were set up to answer three questions:
- Whether an overnight shock clears algae and slime from fouled tubing, and whether repeating it helps
- Whether a low continuous dose holds the lines afterward, and how low that dose can go
- Whether the same approach works on real buildup from a working greenhouse
System Description: Greenhouse Irrigation Lines
The first two trials used lengths of translucent test tubing already fouled with algae, mounted side by side so the inside of each line could be compared directly. The tubing is not optically clear to begin with, so a clean line still reads as pale tan rather than glass clear. Compare each tube against the untreated control beside it, not against what clean water would look like.
The third trial used opaque irrigation tubing cut out of a greenhouse in Virginia, where algae growth inside the line was restricting water flow.
Testing Methodology
Shock treatment trial
- Each treatment was a 50 ppm chlorine dioxide injection, left in the line overnight and flushed out the next morning
- Tubes received one, two, three or four overnight treatments
- One tube was left untreated as a control
Continuous injection trial
- After the shock step, continuous injection ran for the next 22 days
- Four concentrations were held: 0.12 ppm, 0.29 ppm, 0.47 ppm and 1.04 ppm
- One line was left untreated as a control
Field sample: Virginia greenhouse irrigation tubing
- A section of heavily fouled tubing was removed from a greenhouse in Virginia
- It was treated overnight with a 50 ppm chlorine dioxide solution, matching the shock step of the irrigation protocol
- The inside of the pipe was photographed after one night, after two nights, and after four nights
Results
Shock treatment trial
- Every treated tube came back visibly clearer than the untreated control, which stayed green through the trial
- One treatment and four treatments were not visually distinguishable, so what the photographs show is treated against untreated, not a progression
Continuous injection trial
- All four treated lines appeared visibly clearer than the untreated control after 22 days. The control was the only line that had gone back to an olive cast.
- The four dose levels were not visually distinguishable from each other in the photograph
Field sample: Virginia greenhouse irrigation tubing
- The buildup at the start was thick and layered, narrowing the bore of the tubing
- After four overnight treatments, most of the thick buildup was gone and the wall of the pipe was visible again
Discussion
The useful finding from the shock trial is not that more treatments do more. One did the job on test tubing, and the untreated line did not clear on its own. The continuous trial points the same way. All four treated lines looked clearer than the untreated control at 22 days, and the lowest rate tested was 0.12 ppm. The photographs do not separate one dose from another, so what they show is that dosing mattered, not which dose is right.
The field sample is the harder case. Buildup that thick and layered is close to impossible to remove by flushing or brushing, because nothing mechanical reaches the far side of an elbow or the inside of a drip run. Penetrating the slime layer is what made the difference.
Irrigation systems are built from PVC, polyethylene and EPDM, and all three were covered in the material compatibility study, which found no degradation across those materials.
Key Takeaways
What the trials showed
- One overnight shock cleared the test tubing. Heavier buildup, like the Virginia sample, took four nights.
- In both trials, every treated line looked clearer than the untreated control beside it.
- These trials were observational. Results were recorded visually with no microbial counts taken, so they show what cleared, not by how much, and they do not rank one dose against another.
Operating guidance
These are the published use rates for irrigation systems. They are not results from these trials.
- Full cleanout of tanks, lines and emitters: 50 to 100 ppm. Remove or securely cover plants first.
- Continuous dose to keep slime, algae and bacteria from re-establishing once lines are clean: 0.25 ppm.
- Water carrying a heavier organic load: 0.8 ppm continuous.
- Confirm the rate for your own application against the product label and the technical bulletin before setting a program.
For help setting a rate for your own system, email Selective Micro Technologies at inquiry@selectivemicro.com or request wholesale pricing.
See how greenhouse irrigation water treatment keeps lines and emitters clean.