How long can mixed nutrient solution be stored?

Q: 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.

Grower practice

Draft: awaiting expert review Updated 31 October 2026

Also asked

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?

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 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. Irradiated Fe-DTPA nutrient solutions lost both chelate 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 and phosphate and precipitates when A and B are combined strong; at feed strength they stay dissolved ^[2]. Never mix the two concentrates together "to save time".

Warm, still water grows microbes. Pythium 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 ^[4].

pH also drifts in storage as dissolved carbon dioxide 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
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

What to do

Mix what you'll use in a few days.
Store in an opaque, lidded container, out of light.
Keep it cool, ideally 15–20 °C.
Add organic or microbial products on the day you feed.
Stir, then recheck pH and EC before each use.
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 or amino mixes overnight.
Using stored mix without rechecking pH.

Full article: Hydroponic salts explained
Answers: mixing order · topping off the reservoir
Articles: DWC
Terms: stock solution · A-B nutrient · iron chelate

DWC (deep water culture) suspends a plant's roots in an aerated nutrient solution, typically in a bucket with a net pot lid and an air stone.An iron chelate is iron bound to an organic molecule (EDTA, DTPA or EDDHA) that keeps it dissolved and available; each type holds up to a different pH.A chelate is a metal ion held by an organic molecule at several points, keeping micronutrients such as iron, zinc and manganese dissolved and available across a wider pH range.Sulfate (SO4 2-) is the form in which plants take up sulfur, delivered mainly by magnesium sulfate and potassium sulfate in mineral feeds.Phosphate is the ionic form in which plants absorb phosphorus, mainly H2PO4- at the normal root-zone pH of 5.5-6.5.An A/B nutrient is a mineral feed split into two concentrates so that calcium (part A) is kept apart from sulfate and phosphate (part B), which would precipitate together.Input EC is the electrical conductivity of the nutrient solution going into the pot or system, in mS/cm, including the base EC of the source water.A genus of oomycete water moulds, such as Pythium myriotylum and P. aphanidermatum, that cause brown, slimy root rot, especially in warm hydroponic systems.Compost tea is a liquid made by steeping compost or worm castings in water, often aerated with food sources, to extract and multiply microbes for the root zone.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.CO2 enrichment raises carbon dioxide in a sealed grow space from about 420 ppm to roughly 800–1,500 ppm, letting plants use higher light intensities productively.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.Molasses is a sugar-rich by-product of sugar refining added to soil feeds; its sugars feed soil microbes, not the plant, and do not sweeten buds.

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

Albano JP, Miller WB, 2001. Photodegradation of FeDTPA in nutrient solutions. I. Effects of irradiance, wavelength, and temperature. HortScience 36(2):313-316. doi.org/10.21273/HORTSCI.36.2.313

Sonneveld C, Voogt W, 2009. Plant Nutrition of Greenhouse Crops. Springer. doi.org/10.1007/978-90-481-2532-6

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. doi.org/10.1080/07060661.2018.1535466

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. doi.org/10.4315/0362-028X-70.4.828

How long can mixed nutrient solution be stored?

Short answer

Why

The numbers

What to do

Common mistakes

Follow-up questions

Sources

Related quick answers

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