Reagents
What to buy, what to mix, how long it lasts and how the analyzer keeps count.
Buy
| Consumable | Product | Tests / unit | Cost | Notes |
|---|---|---|---|---|
| NO₃ + PO₄ reagents | Neptune Trident NP 2-Month Reagent Kit | 60 of each | $60–84 | Reagent 1, 2, 3a, 3b + calibration solution + waste neutralizer. Ground shipping only, contiguous US. HDPE or glass waste. |
| Alkalinity titrant | 0.1 N HCl, certified (Hach, LabChem, Ricca), 1 L | ~650 after 1:5 dilution | $12–18 | Dilute with DI to 0.02 N; standardise. |
| Alkalinity reference | Na₂CO₃ ACS primary standard | many | $14 | 0.1000 g/L = 1.887 meq/L = 5.28 dKH |
| NO₃ standard | KNO₃ ACS → 1000 ppm NO₃ stock | many | $12 | 1.631 g KNO₃ per litre DI = 1000 ppm NO₃ |
| PO₄ standard | KH₂PO₄ ACS → 100 ppm PO₄ stock | many | $12 | 0.1433 g KH₂PO₄ per litre DI = 100 ppm PO₄; refrigerate, remake monthly |
| pH buffers | 4.00 and 7.00 | — | $10/yr | in the Atlas kit, then 250 mL bottles |
Why the Trident NP kit: it is the only automation-grade liquid nitrate/phosphate reagent set sold to hobbyists. Hanna Checker, Salifert and Red Sea refills are powder packets and cannot be pumped. OpenReef is not affiliated with Neptune; using their reagents in this device is at your own risk and will not be supported by them.
Make calibration standards in nitrate- and phosphate-free saltwater (fresh salt mix with RO/DI), not DI water, so the matrix matches the tank.
Mix (fallback if the kit is unavailable)
Phosphate, APHA 4500-P E
- Reagent A (combined): 50 mL 5 N H₂SO₄ + 5 mL 4 % ammonium molybdate + 15 mL 0.27 % potassium antimonyl tartrate; stable 6 months in HDPE.
- Reagent B: 1.76 g ascorbic acid in 100 mL DI; 1 week refrigerated, or add 2 mL formic acid for ~3 months.
- Dose 400 µL A + 400 µL B per 10 mL. Read at 880 nm after 10 min.
Nitrate, vanadium(III) chloride (Schnetger & Lehners 2014)
- 0.5 g VCl₃ in 100 mL 1 M HCl, then 0.2 g sulfanilamide and 0.01 g NEDD. Dark bottle, refrigerate; 1 month.
- Dose 1000 µL per 10 mL. 30–45 min at room temperature or 10 min at 45 °C. Read at 540 nm.
- Vanadium is toxic: gloves, HDPE waste, chemical-waste disposal.
The same hardware runs either chemistry; only the reagent profile in config.yaml changes (dose volumes, channels, development time). With two reagents per test you need only three syringe pumps.
Accounting
Every dispense subtracts from the bottle’s remaining volume in the database. The API reports remaining millilitres, estimated tests left and raises reagent_low at 10 %. After a bottle change call POST /api/v1/reagents/{id}/refill (optionally with the new volume) and POST /api/v1/reagents/{id}/prime to pull fresh reagent through the line. Run the kit’s calibration solution as a check sample afterwards.
Shelf life and storage
| Reagent | Opened shelf life | Storage |
|---|---|---|
| Trident NP reagents | 2 months (per Neptune) | in the bottle tray, out of sunlight |
| 0.02 N HCl | 3–4 months (evaporation shifts normality) | HDPE, cap with small vent |
| Na₂CO₃ standard solution | 1 month | glass, cool |
| PO₄ / NO₃ stocks | 1 month | refrigerated |
| pH buffers | 6 months after opening | capped |
Handling
- Acid and reagent lines are PTFE; pump tube segments platinum-cured silicone; caps and fittings PP/PETG.
- Waste is collected in a 2 L HDPE bottle with a float switch; add the neutralizer at emptying; never return waste to the tank.
- Reagent bottles sit below the analyzer so a failed check valve cannot siphon reagent into a cell.