# How long can mixed nutrient solution be stored?

> Mixed mineral nutrient solution keeps about a week if it is covered, dark and cool, roughly the same 7-14 days a DWC reservoir runs between changes; an open, warm, lit jug is best used within 1-3 days. Light breaks down chelated iron, warmth grows microbes, and organic or sugary additives spoil within a day or two. Recheck pH and EC before use.

- Canonical: https://genetixbay.com/knowledge/answers/how-long-can-mixed-nutrients-sit.html
- Topic: Nutrients · Type: How-to
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Full article: [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)
- Also asked as: Can I mix nutrients in advance? | How long does premixed nutrient water last? | Is old nutrient solution still good? | Can I store leftover feed for next week? | How long do nutrient concentrates last once opened?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

A covered, dark, cool container of mixed mineral feed stays usable for about a week, in line with the 7–14 days a [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) reservoir runs between changes. An open, warm or lit jug is best used within 1–3 days. Feeds with organic, amino or sugary additives spoil within a day or two. *Grower practice*, backed by the chemistry below.

## Why

Light destroys [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md). Irradiated Fe-DTPA nutrient solutions lost both [chelate](https://genetixbay.com/knowledge/glossary/chelate.md) and soluble iron, which dropped out as a precipitate [1]. A clear jug on a sunny bench is the worst case.

Concentrates are another matter. Calcium meets [sulfate](https://genetixbay.com/knowledge/glossary/sulfate.md) and [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) and precipitates when [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) are combined strong; at [feed strength](https://genetixbay.com/knowledge/glossary/input-ec.md) they stay dissolved [2]. Never mix the two concentrates together "to save time".

Warm, still water grows microbes. [Pythium](https://genetixbay.com/knowledge/glossary/pythium.md) is the classic root pathogen of hydroponic cannabis [3], and warm, stagnant solution suits it. Organic supplements make it worse: kelp, fish and similar additives drove fast bacterial growth in [compost teas](https://genetixbay.com/knowledge/glossary/compost-tea.md) [4].

[pH](https://genetixbay.com/knowledge/glossary/ph.md) also drifts in storage as dissolved [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) exchanges with the air.

## The numbers

| Storage | Usable for | Notes |
|---|---|---|
| Mineral mix, sealed, dark, 15–20 °C (59–68 °F) | ~5–7 days | Recheck pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md) |
| Mineral mix, aerated reservoir, light-proof | 7–14 days | Normal DWC refresh |
| Mineral mix, open or lit, >25 °C (77 °F) | 1–3 days | Iron loss, algae |
| With organics, amino acids or sugars | Same day to 2 days | Ferments, smells |
| Separate A and B concentrates, sealed | Months | Watch for [crystals](https://genetixbay.com/knowledge/glossary/trichome.md) |

## What to do

1. Mix what you'll use in a few days.
2. Store in an opaque, lidded container, out of light.
3. Keep it cool, ideally 15–20 °C.
4. Add organic or microbial products on the day you feed.
5. Stir, then recheck pH and EC before each use.
6. Discard anything cloudy, slimy or smelly.

## Common mistakes

- Storing feed in a clear jug in a lit tent.
- Mixing A and B concentrates together.
- Leaving [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) or amino mixes overnight.
- Using stored mix without rechecking pH.

## Related

- Full article: [Hydroponic salts explained](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)
- Answers: [mixing order](https://genetixbay.com/knowledge/answers/order-to-mix-nutrients.md) · [topping off the reservoir](https://genetixbay.com/knowledge/answers/top-off-reservoir-water-or-nutrients.md)
- Articles: [DWC](https://genetixbay.com/knowledge/systems/dwc.md)
- Terms: [stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md) · [A-B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) · [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md)

## Follow-up questions

**Why does stored nutrient solution go bad?** Stored nutrient solution goes bad in three ways. Light breaks down iron chelates such as Fe-DTPA, dropping soluble iron out as a precipitate. Warm water grows bacteria, fungi and algae, especially when organic, amino or sugary additives are present. And pH drifts as carbon dioxide exchanges with the air. A dark, cool, covered container slows all three.

**Can I mix part A and part B in advance?** You can mix part A and part B in advance only at feed strength, diluted in the full volume of water, never as a combined concentrate. Concentrated together, calcium from part A reacts with sulfate and phosphate from part B and precipitates as gypsum and calcium phosphate, which takes those nutrients out of the feed for good.

**How long do nutrient concentrates last?** Mineral nutrient concentrates kept sealed, separate, dark and cool usually last many months; check the label's date. Watch for crystals, sludge or colour change, which mean something has precipitated or degraded. Organic liquids, amino acids and microbial products have much shorter lives and can ferment or swell, so buy them in amounts you will use within a season.

## Sources

1. Albano JP, Miller WB, 2001. Photodegradation of FeDTPA in nutrient solutions. I. Effects of irradiance, wavelength, and temperature. HortScience 36(2):313-316. https://doi.org/10.21273/HORTSCI.36.2.313
2. Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6
3. 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
4. Ingram DT, Millner PD, 2007. Factors affecting compost tea as a potential source of Escherichia coli and Salmonella on fresh produce. Journal of Food Protection 70(4):828-834. https://doi.org/10.4315/0362-028X-70.4.828