# Biofilm

> A slimy community of microbes stuck to surfaces in a matrix they secrete; in hydro, it coats lines, reservoirs and roots and can shelter pathogens.

- Canonical: https://genetixbay.com/knowledge/glossary/biofilm.html
- Also written: root slime, slime, brown slime, reservoir slime, slimy roots
- Glossary category: Pests and diseases · Evidence: Supported
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A biofilm is a community of bacteria, fungi or algae that attach to a surface and wrap themselves in a sticky matrix of their own polymers. In irrigation and hydroponic systems biofilms coat tubing, emitters, [chillers](https://genetixbay.com/knowledge/glossary/chiller.md), reservoir walls and roots. They are more resistant to disinfectants than free-floating microbes, and can protect pathogens such as *[Pythium](https://genetixbay.com/knowledge/glossary/pythium.md)*.

## In practice

Growers meet biofilm as "root slime": brown or tan gel on roots in [deep water culture](https://genetixbay.com/knowledge/glossary/dwc.md) and [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md), often with a sour smell, or as clogged [drippers](https://genetixbay.com/knowledge/glossary/drip-irrigation.md) and slick lines. Not every biofilm is harmful; beneficial bacteria also form films on healthy roots. Trouble begins when warm, low-oxygen water lets harmful organisms dominate. [Prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md) is light-tight reservoirs, cool well-aerated solution, regular cleaning of lines between runs, and a consistent strategy: either a deliberate [beneficial-microbe reservoir](https://genetixbay.com/knowledge/glossary/beneficial-microbe-reservoir.md) or a fully committed sterile one. GenetixBay prefers the beneficial route, since bacteria arrive regardless.

## Don't confuse with

- **Pythium root rot**: a specific pathogen; slime is often a symptom of it, not the same thing.
- **Algae**: green growth where light reaches the water.
- **Additive staining**: brown colour without slime.

## Related terms

[Root rot](https://genetixbay.com/knowledge/glossary/root-rot.md), [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md), [Sanitation](https://genetixbay.com/knowledge/glossary/sanitation.md), [Shore fly](https://genetixbay.com/knowledge/glossary/shore-fly.md)

## Read more

- [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)
- [Recirculating deep water culture (RDWC)](https://genetixbay.com/knowledge/systems/rdwc.md)

## Sources

1. University of Kentucky Cooperative Extension. Pythium root rot in hydroponic production (E-706). https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/E706.pdf
2. Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. https://doi.org/10.1080/07060661.2018.1535466