# Cloudy, foamy or slimy reservoir: likely causes and fixes

> Cloudy, foamy or slimy reservoir on cannabis is most often Algae from light reaching wet surfaces or the reservoir, Reservoir or root zone too warm or Root rot (Pythium). How to tell them apart, the fix for each and what recovery looks like.

Also called: cloudy res, foam in reservoir, biofilm, slimy tubes, milky water.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=reservoir-cloudy

## Likely causes, most likely first

### Algae from light reaching wet surfaces or the reservoir (Possible)

- Kind: Root zone; urgency: Low urgency
- Fix: Block all light from reservoirs, tubing and the medium surface (opaque lids, covers on rockwool). Clean surfaces between runs. Algae competes for oxygen and feeds gnats and shore flies.
- Recovery: No new green growth within 1-2 weeks of light-proofing.
- Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
- Article: [How do I stop algae in my reservoir or on my medium?](https://genetixbay.com/knowledge/answers/algae-in-reservoir.md)

### Reservoir or root zone too warm (Less likely)

- Kind: Root zone; urgency: Act within a day or two
- Fix: Keep solution at 18-22 °C (64-72 °F): insulate and shade the reservoir, move it off the warm floor or away from the light, use a chiller or frozen water bottles in an emergency, avoid submersible pumps that add heat, cool the room.
- Recovery: Solution holds below 22 °C through the light period; new white roots in 3-5 days.
- Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows.
- Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO.
- Article: [Brown roots in hydroponics (DWC, RDWC, NFT): a differential](https://genetixbay.com/knowledge/diagnosis/root-browning-hydro.md)

### Root rot (Pythium) (Less likely)

- Kind: Disease; urgency: Act now
- Fix: Act now. Fix conditions first: solution at 18-21 °C (65-70 °F), strong aeration (6-8+ mg/L DO), no overwatering. Change the reservoir, trim dead roots with clean scissors, clean and disinfect the system. Then either re-establish beneficial microbes (Bacillus, Trichoderma; house-preferred) or commit fully to a sterile regime (e.g. dosed hypochlorous acid or peroxide). Isolate affected plants on recirculating systems.
- Recovery: New white root tips within 3-7 days and wilting stops; brown roots don't recover.
- Confirm: Look at the roots: Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.
- Confirm: Smell test of roots, medium and reservoir: Smell the roots, the bottom of the root ball, the drain water or the reservoir up close. Healthy roots smell earthy or of nothing. A sour, rotten, swampy or sewage smell means anaerobic conditions and rot. In hydro, a slimy feel on the reservoir walls or tubing adds to the case.
- Confirm: Measure reservoir and root-zone temperature at the end of the light period: Measure the solution in the reservoir and in the root chamber or bucket, at the warmest time of day. Target 18-22 °C (64-72 °F). Above about 23-24 °C (73-75 °F), dissolved oxygen falls and Pythium risk rises; below 16 °C (61 °F) uptake slows.
- Confirm: Dissolved oxygen check: Measure DO with a meter in the root zone, or check the system: air pump running, stones bubbling evenly, return water splashing, no dead spots. Target 6-8+ mg/L. Without a meter: if stones are clogged or the pump is undersized for the volume, assume low DO.
- Confirm: Send a sample to a plant diagnostic lab: For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks.
- Article: [Root rot and Pythium in cannabis](https://genetixbay.com/knowledge/diseases/root-rot-pythium.md)

## Note

Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.