Mixing an Athena Pro Line stock tank (metric)
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Mixing an Athena Pro Line stock tank (metric)

Dissolve a full 25 lb bag of Athena Pro Line into a 50 L stock tank to make a concentrate you dose into your feed later. Covers the chemistry of getting ~227 g/L of salt fully into solution, and why each part needs its own tank.

Feed & mixing6 diagramsEvidence-linked · 6 sources~11 min read
In this guide
01 What a stock tank is, and why you make one02 Accuracy, self-review, and grain-of-salt notes03 The words you need04 Two parts, two tanks, never combine concentrated05 What it takes to dissolve 11 kg in 50 L06 Step-by-step: one bag into one 50 L tank07 Your stock strength, and how to dose it08 What strength to feed, by stage09 Storage & troubleshooting10 What good looks like
Start here

What a stock tank is, and why you make one

This guide covers one job: dissolving a full 25 lb bag of Athena Pro Line into a 50 L tank to make a concentrated stock solution. You don't feed plants with this. It's far too strong. You make it once, then dose small amounts into your watering tank to make the actual feed.

A stock tank turns an awkward powder into an easy liquid. Weighing powder every time you mix feed is slow and inconsistent. Dissolve the whole bag once, then pump or pour a measured number of millilitres per litre into your feed water. Same recipe, every time, in seconds.

The one-sentence version

A full 25 lb (11.34 kg) bag into 50 L makes a stock at about 227 grams per litre, a heavy concentrate. Your whole job is to get every gram truly dissolved, keep the two parts in separate tanks, and know how many millilitres to dose downstream.

Your kit

Written for exactly what you have: a full 25 lb bag, a 50 L tank, jugs of hot water, and a paint-mixer paddle on a drill. The paddle is not optional at this concentration. You cannot hand-stir 11 kg of salt into solution.

How sure is this?

Accuracy, self-review, and grain-of-salt notes

How sure is this paper?

We've gone to great lengths to keep these guides honest. One of the main ways we do that is self-review: we actively look for claims that are subjective, only lightly backed by literature, or based on grower practice rather than a controlled study — and we call those out instead of dressing them up as settled science.

Often there simply is no paper for the decision you're making. In those cases we're drawing on what other growers report and what has worked in our own rooms. That can still be useful — but it is not a lab proof. Do what works for your plants, your room, and your meters. If a table disagrees with your crop, believe the crop and log the difference.

Solid
Well supported by plant science, standards, or broad multi-source consensus
  • A/B separation prevents Ca + sulphate/phosphate precipitation
  • Stock concentration maths for stated bag-into-volume recipes
Operational
What many growers and rooms actually run — start here, then tune
  • Athena Pro Line stock-and-dose workflow as one commercial system among many
Grain of salt
Subjective, thin literature, single studies, or “this works for us” practice
  • Any third-party dosing table not verified with your meter and water

See something glaringly wrong? Tell us and we'll fix it. Please open a GitHub issue with the paper name and what looks off (include a source if you have one): Report an accuracy issue. Local law, labels, and licences always override any recipe here. Inline notes labelled grain of salt flag the highest-risk over-trust points in the text.

Vocabulary

The words you need

Stock solution (concentrate)A strong nutrient solution you store and dose from. Here, one whole bag in 50 L. Never fed to plants neat.
Working solution (feed)The diluted solution the plants actually drink, made by dosing a little stock into a lot of water.
Part A / Pro CoreThe calcium-and-nitrogen base of Athena Pro Line. Gets its own stock tank.
Part B / Pro Grow or Pro BloomThe part carrying sulfates and phosphates. Gets a separate stock tank from Part A.
Dosing rateHow much stock you add per litre of feed water, in millilitres per litre (mL/L). This is what you use day to day.
Solubility / saturationHow much salt a given volume of water can hold. Warmer water holds more. Past its limit, salt won't dissolve and sits as grit[3].
Precipitation / lockoutWhen dissolved salts react and fall out as solid, for example calcium meeting sulfate or phosphate. The nutrient leaves the water and the plant can't use it[2].
EC (electrical conductivity)A meter reading of total dissolved salt. This is how you check the strength of your finished feed.
The one rule

Two parts, two tanks, never combine concentrated

Part A and Part B each get their own stock tank, and the two concentrates must never touch. This is the rule that saves your crop and your pump. One 25 lb bag of Pro Core → one 50 L tank. One 25 lb bag of Pro Grow/Bloom → a different 50 L tank.

The reason is chemistry. Part A is loaded with calcium. Part B carries sulfates and phosphates. In a dilute feed that's fine, but if you pour the two concentrates together the calcium instantly grabs the sulfate and phosphate and drops out as solid gypsum and calcium phosphate[1]. You get a tank of useless sludge and a crop starved of the very nutrients you just added[2].

Where the two parts are allowed to meet1Bag A to Tank APro Core stock,alone→2Bag B to Tank BGrow/Bloomstock, alone→3Feed waterdose A in, stir→4Same waterthen dose B in,stir→5Plantsnow dilute &safeThey only ever meet heavily diluted, in the feed water, added one at a time.
Figure 1. Concentrated A plus concentrated B gives an instant precipitate. Diluted, added separately to feed water, they coexist fine. That gap is the whole rule.
Never do these
  • Never pour Part A stock into Part B stock (or vice-versa).
  • Never add the two concentrates to feed water at the same moment. Add A, stir, then add B, stir.
  • Never reuse a dosing jug between A and B without rinsing.
The why

What it takes to dissolve 11 kg in 50 L

227 grams of salt per litre is a lot, roughly six to seven times saltier than seawater. Getting it fully into solution isn't automatic. Two bits of physics work against you.

  • Dissolving cools the water. Most of these salts pull heat in as they dissolve (endothermic), so the tank gets colder as you add powder, and colder water dissolves less[3]. Hot water and a paddle beat that downward spiral.
  • Cold or still water saturates. Without heat and vigorous mixing, you hit the saturation limit and the last of the bag sits as grit on the bottom, leaving an underdosed, inconsistent stock.
Warmer water dissolves more saltWhy you start with hot water: solubility climbs with temperature, and dissolving cools the tank.027538010610C20C30C40C50Crelative amount dissolvable
Figure 2. Solubility rises with temperature, so hot water both holds more and offsets the cooling the dissolving salt causes[3].
Hot, not boiling

Use hot tap water (about 40-50 °C), not boiling. Boiling water can damage some compounds and is a scald hazard with a spinning paddle. Warm is enough to win the solubility fight.

The method

Step-by-step: one bag into one 50 L tank

Do this once per part: once for the Pro Core bag (Tank A), once for the Pro Grow/Bloom bag (Tank B). Same steps each time.

  1. 1
    Start with hot water, ~40 L
    Fill the 50 L tank to about 40 L with hot water (about 40-50 °C). Leave headroom. 11 kg of powder takes up real volume and you still need room to mix without slopping.
  2. 2
    Start the paddle before adding powder
    Get the paint-mixer turning a vortex first. You want the salt landing in moving water, not piling on a still bottom.
  3. 3
    Add the bag gradually
    Pour the powder in slowly, a steady stream, not the whole bag at once. Dumping it causes clumps that trap dry powder inside (a 'fish-eye') that never dissolves.
  4. 4
    Mix until perfectly clear
    Keep mixing until there is zero grit and the solution is clear (it may be tinted). At this concentration this can take several minutes of active mixing, not seconds.
  5. 5
    Top up to exactly 50 L
    Once fully dissolved, top with warm water to the 50 L mark. Topping up after dissolving keeps your concentration exact.
  6. 6
    Label and date the tank
    Mark it 'PART A, Pro Core' or 'PART B, Grow/Bloom' plus the date. Mixing up two near-identical tanks is how the cardinal rule gets broken.
  7. 7
    Let it cool and settle, then re-check
    As it cools, watch for anything dropping out. A little fine sediment can mean you were at the edge of saturation. Re-mix. If it persists, the bag may need slightly more volume.
The fixed sequence (per bag)1Hot water ~40 Lfill first→2Paddle onmake a vortex→3Add bag slowlysteady stream→4Mix to clearzero grit→5Top to 50 Lexact strength→6Label A or Band dateIdentical for both bags - just two separate, clearly-labelled tanks.
Figure 3. The whole method on one line. Run it twice: once per bag, into two separate tanks.
The numbers

Your stock strength, and how to dose it

A full 25 lb bag is 11.34 kg. In 50 L that gives a stock of:

Stock concentration from a full bag in 50 L11.34 kg / 50 L = 226.8 g/L. That's your concentrate strength.065130195260227 gPer litre23 gPer 100 mL
Figure 4. 11.34 kg in 50 L = 226.8 g/L. Knowing this one number lets you convert your bag's printed feed rate into a simple millilitres-per-litre dose.

To use it, you dilute. If your bag (or Athena's chart) says to feed a part at a rate of X grams per litre of finished feed, then because your stock is 226.8 g/L:

The dosing formula

Dose (mL of stock per L of feed) = feed rate (g/L) ÷ 226.8 × 1000 ≈ feed rate × 4.41[6]. Do this separately for Part A and Part B using each part's own rate.

Dosing your 226.8 g/L stock. Always confirm the target rate on your bag - formulas change.
If the label feed rate is......dose this much stock per litre of feed
0.5 g/L2.2 mL/L
1.0 g/L4.4 mL/L
1.5 g/L6.6 mL/L
2.0 g/L8.8 mL/L
Always finish on a meter

Dosing math gets you close. Your EC meter confirms it. Mix the feed, read EC, and trust the meter over the calculator, because water and formulas vary[7].

Downstream

What strength to feed, by stage

The stock is only a delivery system. The plant cares about the feed strength, read as EC. Young plants want it weak, bulking plants want it strong, and you taper at the end. Cannabis nutrient demand genuinely shifts across the cycle[4].

Rough feed-EC targets by stageIndicative bands - run your own meter and follow Athena's chart for your cultivar.clones / seedlingvegflower bulklate / taper0.8 EC2.4 EC4 EC
Figure 5. Feed weak early, build through veg and flower, taper late[5]. These are starting bands, not law. Substrate and strain shift them.
Over-feeding is its own stress

Cranking EC does not mean more growth. Too much salt in the root zone pulls water back out of the roots (osmotic stress) and burns the plant[8]. When in doubt, feed slightly weaker.

When it goes wrong

Storage & troubleshooting

SymptomLikely causeWhat to do
Grit on the tank bottomHit saturation - water too cold or under-mixedRe-mix with the paddle; warm it; if it won't clear, add a little more volume
Crystals form in storageStock cooled and dropped out near saturationWarm gently and re-mix before dosing; store somewhere not cold
Cloudy / milky stockPossible cross-contamination of A into BSuspect a precipitate - do not feed; check your jugs/labels[1]
Feed EC lower than the math predictsBag didn't fully dissolve / underdosed stockConfirm stock fully dissolved; recalibrate the EC meter
Sludge after combiningConcentrates A and B were mixedDiscard - this is precipitated, unusable; never combine concentrates
Storage

Keep each stock tank sealed, labelled, out of cold and out of light. Mix before each use in case anything has settled. Make what you'll use in a reasonable window rather than a year's supply[7].

Straight talk

What good looks like

Remember
  1. Two bags, two tanks, never combined concentrated. This is the rule that prevents ruined stock.
  2. Hot water + the paddle + patience get all 226.8 g/L truly dissolved - clear, zero grit.
  3. Stock is for dosing, not feeding. Dilute to an EC target and confirm on a meter, every time.
  4. Match feed strength to stage, and remember stronger isn't better[8].

Once your stock is made, the day-to-day is dosing into feed water and watering well. See coco & crop steering for how that feed behaves in the root zone, and the irrigation manual for delivering it.

Related papers
Coco & crop steering
Steer the plant with water
Irrigation manual
Install and run the system
Root-zone state · TEROS-12
What the sensor really sees

References

  1. Guan, W. (2017). Fertilizer Compatibility. Purdue University Vegetable Crops Hotline, Issue 643. Purdue Extension. (industry/manufacturer or non-journal source) https://vegcropshotline.org/article/fertilizer-compatibility/
  2. Fernandez, D. (2020). Using Calcium Sulfate in Hydroponics. Science in Hydroponics. (industry/manufacturer or non-journal source) https://scienceinhydroponics.com/2020/06/using-calcium-sulfate-in-hydroponics.html
  3. LibreTexts Chemistry. Temperature Effects on Solubility (Physical & Theoretical Chemistry; Equilibria/Solubility module). (industry/manufacturer or non-journal source) https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Solubilty/Temperature_Effects_on_Solubility
  4. Saloner, A., & Bernstein, N. (2023). Dynamics of Mineral Uptake and Plant Function during Development of Drug-Type Medical Cannabis Plants. Agronomy, 13(12), 2865. https://doi.org/10.3390/agronomy13122865
  5. Saloner, A., & Bernstein, N. (2024). Mineral nutrition for Cannabis sativa in the vegetative stage using response surface analysis. Frontiers in Plant Science, 15, 1501484. https://doi.org/10.3389/fpls.2024.1501484
  6. Powell, K., & Bauerle, W. L. (2026). Predicting vegetative phase nutrient uptake in Cannabis sativa L. via transpiration-driven mass-balance. Frontiers in Plant Science, 16, 1753553. https://doi.org/10.3389/fpls.2025.1753553
  7. Hultberg, M., et al. / van Os, E. (2004). Water quality assessment of different reservoir types in relation to nutrient solution use in hydroponics. Agricultural Water Management (Elsevier ScienceDirect). https://www.sciencedirect.com/science/article/abs/pii/S0378377404001908
  8. Yep, B., Gale, N. V., & Zheng, Y. (2020). Aquaponic and Hydroponic Solutions Modulate NaCl-Induced Stress in Drug-Type Cannabis sativa L. Frontiers in Plant Science, 11, 1169. https://doi.org/10.3389/fpls.2020.01169

Citations marked in-text as [n] map to this list. Primary literature and official guidance except where noted. Cannabis tissue culture is strongly genotype-dependent, verify dilutions, hormone doses and local regulations against the primary sources before relying on them.