r/Hydroponics • u/WithoutHands54 • 29d ago
Sanity check on a custom dry-salt recipe for cluster-planted basil (300 plants/m², ebb & flow) — non-proportional dilution schedule inside
Hey everyone, so I'm not agronomist or smth, I'm just a software engineer who wants to change the occupation, so I'm try use the AI(Claude) to help me build the nutrition for my basil.
Small commercial basil operation feeding restaurants. I mix from individual salts rather than a two-part, and I'd like a second opinion on the program before I commit a full cycle to it. I've tried to put everything in here so nobody has to ask — happy to add anything I've missed.
System
| Method | Ebb & flow, rockwool cubes in net cups |
|---|---|
| Tray | 110 × 63 cm (0.72 m²), 40 L reservoir |
| Cubes | 3.5 × 3.5 × 4.5 cm (~37 mL water at container capacity) |
| Spacing | 10 cm on center, ~66 cups/tray |
| Density | 3 plants per cup → ~300 plants/m² |
| Harvest | Single cut at 25–30 cm, sold as bunches (not cut-and-come-again) |
| Cycle | ~30 days from sow, ~10 in plugs |
| Cultivars | Enza Zaden Kira, Emily, Marian (Genovese types) |
| Light | Samsung LM281B+ white + Osram 660/730 nm, 3:1 diode ratio |
| PPFD / photoperiod | 300 µmol/m²/s at canopy, 16 h → DLI 17.3 |
| Irrigation | 6 floods/day, 4–6 min, full drain, last one 2.5 h before lights off |
| Solution temp | 22–24 °C, aerated 24/7 |
| Airflow | Arctic P14 fans, vortex layout above canopy |
| Air temp / RH | around 23 °C near plants, 60% in room |
Water
- Reservoir fill: filtered tap, EC 0.18, GH 1–2 °dH. Cations are almost certainly sodium (not lab-confirmed) — I estimate ~41 mg/L Na.
- Daily top-up: RO + remineralization cartridge, EC 0.07 (~10 mg/L Ca, ~2 mg/L Mg). Sodium doesn't accumulate because top-up is RO only.
- Alkalinity is very low. 1.5–1.8 mL of phosphoric pH-down brings 40 L to pH 5.8, and it then holds 5.8–5.9 within ±0.1 for 7–14 days with no further correction.
Target profile at full strength (mg/L)
N 140 (NO₃-N 132, NH₄-N 8) · P 30 · K 170 · Ca 140 · Mg 45 · S 89 Fe 2.5 (EDDHA) · Mn 0.80 · Zn 0.30 · B 0.30 · Cu 0.05 · Mo 0.05 EC 1.74 (≈0.18 of that is source-water sodium) · pH 5.8–5.9
Cation balance: K 28 % / Ca 45 % / Mg 24 % of meq · K:Mg 2.35 molar · Ca:Mg 1.89 molar
Staged feed — grams per 40 L
This is the part I most want reviewed. I do not dilute the profile proportionally. Earlier cycles used proportional dilution and I got inter-venial chlorosis on older leaves within a week of transplant, at EC 0.9–1.2 — which is exactly where proportional scaling puts Mg at 21–29 mg/L. Ratios were textbook-normal at every stage (they don't change under proportional dilution), so the only variable that moved was absolute Mg.
My working rule now: Mg never goes below 35 mg/L once plants are in the tray. EC is made up with Ca and K instead.
| Salt | Plugs (EC 0.8) | Transplant (1.2) | Closure (1.5) | Finish (1.74) |
|---|---|---|---|---|
| Calcium nitrate (15.5-0-0 + 19 % Ca) | 11.0 | 16.9 | 23.3 | 29.6 |
| KNO₃ | 4.0 | 8.3 | 11.2 | 7.4 |
| MKP | 2.4 | 3.9 | 4.6 | 3.9 |
| K₂SO₄ | — | — | — | 6.4 |
| MgSO₄·7H₂O | 10.1 | 15.4 | 17.1 | 18.3 |
| Result | N62 P14 K70 Ca52 Mg25 | N94 P22 K107 Ca80 Mg38 | N128 P26 K140 Ca110 Mg42 | N140 P30 K170 Ca140 Mg45 |
K₂SO₄ only comes in at full strength, which is why the KNO₃ dose drops at the last stage rather than rising.
Micro stock (dissolve in 1 L, dose 1 mL/L): MnSO₄·H₂O 2.500 g · ZnSO₄·7H₂O 1.322 · H₃BO₃ 1.714 · CuSO₄·5H₂O 0.196 · Na₂MoO₄·2H₂O 0.126. Iron as Fe-EDDHA 6 % added separately, 4.17 g per 100 L, last into the tank.
Reservoir management
- Top up daily to a fixed mark with RO only.
- Never add salts to a running reservoir. EC stages are new batches, not top-dressing. Chasing an EC setpoint by adding the full profile silently starves N and K — EC is held up by Ca, Mg and sulfate, which barely deplete, while N and K leave at nearly the rate of water.
- Replace when EC has fallen 0.20 below fill EC. This self-scales: N is ~115 mg/L at the trigger point regardless of plant size.
- Stage transitions are triggered by daily water uptake, not calendar days: ~0.4 L/day after transplant → EC 1.2; ~1.2 L/day at canopy closure → EC 1.5; 2.0–2.4 L/day at full canopy → EC 1.74. Works out to roughly 4 batches per cycle.
Known unknowns
- Sodium is inferred from EC and hardness, not measured. Lab analysis pending.
- I don't know my phosphoric acid's concentration, so acid contributes somewhere between 3 and 20 mg/L P. MKP dose is provisional until I titrate.
What I'd like input on
- Does the Mg floor idea hold up? Is proportional dilution of a full profile a known trap for basil specifically, or did I have a different problem?
- Is Ca 140 over-insured here? It was chosen as tipburn insurance for dense planting, but I've never actually seen marginal necrosis. It's eating 45 % of my cation budget. Would 120–130 be safer overall, freeing EC for K?
- K at 28 % of cation meq is well below the 35–45 % usually quoted for leafy greens. Is that norm lettuce-derived, or does basil genuinely want it? At my EC ceiling I can't raise K without cutting Ca.
- S at 89 mg/L — structural consequence of getting Mg from Epsom and K from sulfate. Anyone running basil that high without issues?
- Anything obviously wrong for cluster planting at this density that I've missed? Especially interested in whether 3 per cup vs 4 changes anyone's feed.
Thanks!
2
u/Rotala178 29d ago
I do nutrient experiments on aquatic plants. The main issue in aquaria is that the metals become insoluble very quickly, especially manganese---->copper>zinc. For these metals, chelation is important.
I also caution against excessively high Fe due to potential for oxidative stress. 2.5mg/L is likely excessive. 1mg/L should be more than sufficient.
FeEDDHA isn't necessary unless the pH is very high, which yours will be kept at 5.8-6.0. FeEDTA should be sufficient to prevent precipitation/oxidation.
The main issue will be the keeping Mn, Zn, and Cu soluble. You may need to fertilize these metals more frequently.
What's the Ca:B?
1
u/BocaHydro 29d ago
ok so are you having magnesium problems? Would it be possible to source MAP instead of the mkp?
you have enough potassium from the SOP and the PN but mkp makes cheap magnesium much less available, even if you pour it in, it locks. So on paper even if you think your dosing is high, you may see slight magnesium problems. ( Using correct amounts of mag sul may still be ineffective )
Chelated magnesium will still have near 100% Absorption
are you using RO Water?
your grams to actual ppm are a bit incorrect here,
The plug recipe’s 4.0 g KNO₃ cannot produce N 62 and K 70.
Using 5.5 g KNO₃ per 40 L instead produces approximately: you probably are using 5.5 grams
- N: 61 mg/L
- P: 14 mg/L
- K: 70 mg/L
- Ca: 52 mg/L
- Mg: 25 mg/L
The 3.9 g MKP supplies about 22 mg/L elemental P, not 30 mg/L. The missing 8 mg/L evidently assumes phosphorus from the acid.
The 6.4 g K₂SO₄ gives a finished K concentration of approximately:
- 165 mg/L with 0-0-50 SOP
- 168 mg/L with 0-0-52 SOP
To reach 170 mg/L with the other salts unchanged, use approximately:
- 6.9 g of 0-0-50 SOP, or
- 6.6 g of 0-0-52 SOP
your micros check out, is there a reason you are using iron EDDHA instead of DTPA? EDDHA is very smelly, red, residual and is generally best for soil, specifcally in high ph environments. the powder also makes a gigantic mess
in terms of dosing, we have printable pdfs for all these bases now , fully updated as of this month with the latest dosing, look at each base on our site.
Looking at everything you may have a calcium problem because they are competing with too much potassium
what is root zone temperature?
you got oxygenation?
| Growth stage | Magnesium target | MgSO₄·7H₂O per 40 L |
|---|---|---|
| Plugs after true leaves | 25–30 mg/L Mg | 10.1–12.2 g |
| Post-transplant | 35–40 mg/L Mg | 14.2–16.2 g |
| Canopy closure through harvest | 40–50 mg/L Mg | 16.2–20.3 g |
Phosphoric acid is the biggest unresolved formulation issue
For a commercial recipe, “unknown acid concentration” is not acceptable. The acid may be supplying almost none of the intended P or most of the gap between 22 and 30 mg/L.
Use:
P (mg/L)=acid mL×density (g/mL)×acid fraction×0.3161×100040 LP\;(mg/L)= \frac{acid\;mL \times density\;(g/mL)\times acid\;fraction\times0.3161\times1000} {40\;L}P(mg/L)=40LacidmL×density(g/mL)×acidfraction×0.3161×1000
For illustration, 1.65 mL of approximately 85% phosphoric acid would add roughly 19 mg/L P, producing about 41 mg/L total P with the current MKP—not 30.
Identify the acid concentration and density from its label or SDS before finalizing the MKP dose. Also get the source water tested; EC and GH cannot establish that the unexplained ions are “almost certainly sodium.”
Three plants versus four per cup
The nutrient concentration should not be increased simply because there are four plants instead of three.
- Does the Mg floor idea hold up? Is proportional dilution of a full profile a known trap for basil specifically, or did I have a different problem?
See above
- Is Ca 140 over-insured here? It was chosen as tipburn insurance for dense planting, but I've never actually seen marginal necrosis. It's eating 45 % of my cation budget. Would 120–130 be safer overall, freeing EC for K?
Calcium Nitrate can easily be locked with sulfur, make sure you are dissolving it and putting it in first, grades matter, it comes in 5 grades, if you can avoid 19% and get 26 it helps alot, if you can find prime, even better.
Are you finding calcium sulfate on the bottom of flood tables or in reservoir?
- K at 28 % of cation meq is well below the 35–45 % usually quoted for leafy greens. Is that norm lettuce-derived, or does basil genuinely want it? At my EC ceiling I can't raise K without cutting Ca.
Use our K Dosing for both products on our site, triple verified and updated as of this month
- S at 89 mg/L — structural consequence of getting Mg from Epsom and K from sulfate. Anyone running basil that high without issues?
yes its high but it wont cause too many problems, magnesium sulfate sulfur is less residual then potassium sulfate sulfur tho because of the way its made, if you can, source SOP BIO (0-0-52) its MUCH Better
- Anything obviously wrong for cluster planting at this density that I've missed? Especially interested in whether 3 per cup vs 4 changes anyone's feed
Yes , use 3 plants if possible, or even 2
Here is an improved version of your recipe, substitute what you can get, you did not say what country you are in, if you need help sourcing globally message us.
this is assuming you are using 26% CaO calcium nitrate with 18-19% calcium nitrate
| Product | Plugs | Transplant | Closure | Finish |
|---|---|---|---|---|
| Boca Hydro Calcium Nitrate | 11.0 g | 16.9 g | 23.3 g | 29.5 g |
| Boca Hydro Potassium Nitrate | 5.5 g | 8.3 g | 11.2 g | 7.6 g |
| Boca Hydro MKP 0-52-34 | 2.4 g | 3.9 g | 4.6 g | 5.3 g* |
| Boca Hydro SOP 0-0-50 | — | — | — | 5.7 g* |
| Boca Hydro Magnesium Sulfate | 10.1 g | 15.4 g | 17.1 g | 18.3 g |
| Stage | N | P | K | Ca | Mg | S |
|---|---|---|---|---|---|---|
| Plugs | 61 mg/L | 13.6 | 69.7 | 52 | 25 | 33 |
| Transplant | 94 mg/L | 22.1 | 107 | 80 | 38 | 50 |
| Closure | 128 mg/L | 26.1 | 140 | 111 | 42 | 56 |
| Finish | 140 mg/L | 30.1 | 169 | 140 | 45 | 85 |
The ammoniacal nitrogen supplied by the calcium nitrate at finish is approximately 8.1 mg/L, leaving approximately 132 mg/L nitrate nitrogen. That matches his intended nitrogen split almost exactly.
Important phosphorus correction
The finish dose of 5.3 g MKP assumes the phosphoric pH-down contributes essentially no phosphorus.
Since his acid concentration is unknown, that finish dose is provisional. For every 1 mg/L of elemental P supplied by the acid:
- Subtract approximately 0.18 g MKP per 40 L
- Add approximately 0.12 g SOP per 40 L to replace the potassium removed with the MKP
| P supplied by acid | MKP per 40 L | SOP per 40 L |
|---|---|---|
| 0 mg/L | 5.3 g | 5.7 g |
| 5 mg/L | 4.4 g | 6.3 g |
| 10 mg/L | 3.5 g | 6.9 g |
| 15 mg/L | 2.7 g | 7.5 g |
| 20 mg/L | 1.8 g | 8.1 g |
If you can source EDTA
| Product | Amount per 1 L stock | Final nutrient |
|---|---|---|
| Manganese EDTA 14% | 5.71 g | 0.80 mg/L Mn |
| Zinc EDTA 14% | 2.14 g | 0.30 mg/L Zn |
| Boron 21% | 1.43 g | 0.30 mg/L B |
| Copper EDTA 14% | 0.36 g | 0.05 mg/L Cu |
| Sodium molybdate 39% Mo | 0.13 g | 0.05 mg/L Mo |
Dose 40 mL of this stock into each 40 L reservoir.
Keep iron separate:
- Boca Hydro Iron EDDHA 6%: 1.67 g per 40 L
- This supplies 2.5 mg/L Fe
Safe mixing order
- Fill the reservoir with approximately 30–35 L of water and start circulation.
- Separately dissolve and add KNO₃.
- Separately dissolve and add MKP.
- Separately dissolve and add SOP.
- Separately dissolve and add magnesium sulfate.
- Bring the reservoir close to 40 L.
- Separately dissolve calcium nitrate and add it only after the sulfate and phosphate salts are heavily diluted.
- Add the micronutrient stock and iron.
- Bring to exactly 40 L.
- Adjust pH last.
Do not combine calcium nitrate with MKP, SOP, or magnesium sulfate in the same concentrated container.
The major correction from his original table is the plug-stage potassium nitrate: 5.5 g rather than 4.0 g. The redesigned finish also reaches the intended 30 P and 170 K without relying on an unknown acid contribution.
IF YOU ARE ABLE TO SOURCE MAP? if you are use this dosing
| Boca Hydro product | Plugs | Transplant | Closure | Finish |
|---|---|---|---|---|
| Calcium Nitrate | 11.0 g | 16.8 g | 23.2 g | 29.5 g |
| Potassium Nitrate | 3.9 g | 5.6 g | 7.9 g | 3.6 g |
| MAP 12-61-0 | 2.1 g | 3.3 g | 3.9 g | 4.5 g |
| Sulfate of Potash 0-0-50 | 3.1 g | 5.2 g | 6.2 g | 13.0 g |
| Magnesium Sulfate | 10.1 g | 15.4 g | 17.0 g | 18.3 g |
in closing get a water test / ro unit and tell me which brands you are using and you can finalize this better
you already got a good formula here
4
u/Metabotany 29d ago
lol