Source-water chemistry
Measure pH, alkalinity or bicarbonate, calcium, magnesium, sulfate, sodium, chloride and EC before calculating fertilizer contributions.
Fertigation compatibility guide
Greenhouse Fertilizer Stock Tank Compatibility
Keep concentrated calcium away from incompatible phosphate and sulfate sources, then verify the A/B design against source water, concentration, temperature and injection conditions.
Decision guide
Prevent precipitation in the concentrate, not after emitters clog
A fertilizer recipe that is stable after dilution may still precipitate when the same salts are held together at stock-tank concentration.
The recurring conflicts are calcium with phosphate and calcium with sulfate. Insoluble material removes nutrients from solution and can settle in tanks, strainers, injectors and emitters. Separate A/B concentrates are therefore a design requirement whenever incompatible salts would otherwise meet at high concentration.
Phosphate choice is not interchangeable. MKP contributes phosphorus and potassium without nitrogen; MAP adds ammonium nitrogen; DKP carries a different potassium-to-phosphorus contribution and alkalinity behavior. Selection must fit the complete nutrient balance, water analysis and target root-zone pH and EC.
Evidence path: calculate the full recipe, assign incompatible salts to separate stocks, test each concentrate over its intended holding time, then verify clarity, pH, EC and nutrient delivery after injection.
Compatibility inputs
What changes the precipitation risk?
Stock concentration magnifies interactions that may not appear in the final irrigation solution.
Stock concentration and hold time
Record the injector ratio, batch volume, temperature and maximum storage period; concentrated or cold solutions can expose solubility limits.
Complete nutrient balance
Account for every source of N, P, K, Ca, Mg, S and micronutrients rather than choosing a phosphate on phosphorus content alone.
Injection and mixing
Confirm separate pickup points, dilution water flow, mixing order, backflow protection and the distance before incompatible streams meet.
A/B tank planning
Separate incompatible salts, then choose the phosphate by nutrient contribution
This is a compatibility map, not a universal fertilizer recipe. Final placement depends on all ingredients and the actual concentrate strength.
| Component or decision | Practical placement or role | What to verify |
|---|---|---|
| Calcium nitrate | Keep in a calcium stock away from concentrated phosphate and sulfate sources; iron chelate placement depends on the chelate and program | Clarity over hold time, calcium assay, temperature, injector calibration and absence of cross-contamination |
| Phosphate and sulfate salts | Place in the non-calcium stock unless compatibility testing supports another arrangement | Solubility at stock concentration, sediment, pH drift and compatibility with micronutrients |
| MKP | Phosphorus and potassium source without ammonium nitrogen | Total P and K balance, grade solubility, insolubles and final root-zone pH and EC |
| MAP | Phosphorus source that also contributes ammonium nitrogen | Ammonium share of total N, crop-stage fit, water pH and downstream nutrient balance |
| DKP | Phosphorus and potassium source with a different nutrient ratio and solution behavior from MKP | K and P balance, concentrate pH, solubility and compatibility with the rest of the non-calcium stock |
| Source-water bicarbonate, Ca and Mg | Treat as part of the formulation, not as blank dilution water | Acid demand where used, carbonate precipitation risk, delivered alkalinity and emitter deposits |
Compatibility trial
Test the actual concentrate and injector ratio
A beaker of dilute feed solution cannot establish whether a stock will remain usable for several days.
Calculate before mixing
Convert the crop target and source-water contribution into final and stock concentrations for every nutrient source.
Make representative stocks
Use production water, intended grades, mixing order, concentration, temperature and container material.
Observe the full hold time
Check immediate haze and delayed sediment; record pH, EC, clarity and any material retained by a defined filter.
Verify after injection
Sample representative emitters and confirm injector ratio, nutrient delivery, pH, EC and deposit formation through an operating cycle.
Acceptance evidence
Measure compatibility where failure occurs
Tank clarity alone is useful but incomplete; the injector and delivered solution must also remain within specification.
Concentrate stability
Record initial and aged clarity, sediment, filter residue, pH and EC at the intended concentration and temperature.
Injector delivery
Calibrate the injection ratio and compare pH and EC at the mixing point and representative emitters.
Nutrient recovery
Where risk or value warrants, analyze key nutrients after preparation and holding to detect losses hidden by visual inspection.
Operating cleanliness
Inspect strainers, pickup tubes, injectors and emitters for deposits and distinguish chemical precipitate from insoluble anticaking residue.
Raw-material RFQ
Request data that affects stock-tank performance
Product name and N-P-K declaration alone do not show whether a grade will dissolve and remain usable in the intended concentrate.
Recipe and water
Provide source-water analysis, crop stage, final nutrient targets, all fertilizer salts, acids and micronutrients.
Stock design
State A/B assignments, injector ratio, batch size, water temperature, mixing order and maximum hold time.
Grade controls
Request assay, moisture, water insolubles, relevant impurities, particle form, COA, TDS, SDS and lot consistency information.
Acceptance test
Define dissolution time, allowable residue or sediment, delivered pH and EC, packaging, trial volume and commercial demand.
Grower and formulator questions
Greenhouse fertilizer stock tank FAQ
Why are calcium and phosphate kept in separate stock tanks?
At concentrate strength they can form sparingly soluble calcium phosphate. Separation allows the streams to meet only after substantial dilution in flowing irrigation water.
Should calcium also be separated from sulfate?
Yes when concentrate conditions can produce calcium sulfate. The full formula, source water, concentration and temperature determine the practical risk.
Are MKP, MAP and DKP interchangeable phosphate sources?
No. They contribute different accompanying nutrients and have different solution behavior. Choose them through the complete N-P-K balance, pH strategy, crop stage and compatibility trial.
Can a clear stock tank still deliver the wrong nutrient concentration?
Yes. Injector calibration, formulation errors or dissolved losses not visible to the eye can change delivery. Verify the diluted solution at representative emitters.
Related decision paths
Continue from compatibility to raw-material qualification
Use these guides to connect nutrient strategy, fertilizer-grade controls and individual phosphate identities.
Technical and commercial inquiry
Prepare your RFQ Share the data behind your application target.
Include the process, current problem, target market, trial volume, annual demand and required documents.