Open hardware · Reef chemistry · v2.0
OpenReef is an open-source analyzer you build from off-the-shelf parts for about $849. It titrates alkalinity the way oceanographers do, reads nitrate and phosphate by self-blanked colorimetry, and exposes every result through a full REST API.
How it measures
A 20 mL sample is titrated with 0.02 N HCl in 60 µL steps while a lab-grade electrode tracks pH. The excess-acid region is extrapolated to the equivalence point, with a DIC correction, so electrode offset drops out of the result.
Method & math →The cell is read before and after reagent so turbidity and colour cancel. An 850 nm LED and an 11-channel spectral sensor resolve 0.01 ppm PO₄ in a 22 mm cuvette.
Optics & chemistry →Nitrate is reduced and coupled into a pink azo dye read at 540 nm. Reagent kinetics are characterised on your own standards, so any liquid kit — Trident NP or lab-mixed — can be profiled.
Reagent options →Hardware
Every part is something you can order today. The syringe pumps are a NEMA17, a T8 lead screw and a 5 mL glass syringe between two check valves — 0.07 µL per step. Six cheap peristaltic pumps move sample and waste; a dip tube sets the volume so no pump needs to be precise except the ones that are.
| Parameter | Range | Resolution | Cycle |
|---|---|---|---|
| Alkalinity | 4–14 dKH | 0.02 dKH | 6–8 min |
| Phosphate | 0–1.0 ppm | 0.01 ppm | 10–12 min |
| Nitrate | 0–50 ppm | 0.1 ppm | 15–30 min |
| Sample per alk test | ≈75 mL tank water, 1.5 mL 0.02 N HCl | ||
| Reagent autonomy | 60 days NO₃/PO₄ at 1/day (Trident NP kit) · 2+ months acid | ||
| Power | 12 V DC, <30 W peak | ||
Parts
Software
One Python service runs the fluidics, the chemistry math, a scheduler, SQLite history and the dashboard. Every result keeps its raw titration curve or absorbance channels and a quality score. A hardware simulator with a carbonate-system model runs the whole stack on a laptop.
$ curl -s -H "X-API-Key: $KEY" http://openreef.local:8080/api/v1/results/latest
{
"alkalinity": { "value": 8.29, "unit": "dKH", "quality": 0.98, "ts": 1794093600 },
"phosphate": { "value": 0.08, "unit": "ppm", "quality": 1.00, "ts": 1794072600 },
"nitrate": { "value": 5.1, "unit": "ppm", "quality": 0.95, "ts": 1794074400 }
}
$ curl -s -X POST -H "X-API-Key: $KEY" http://openreef.local:8080/api/v1/tests/alkalinity
{ "run_id": 418, "test": "alkalinity", "status": "started" }Build path
Order the BOM, print five pump frames, two cell parts and the brackets, cut the panels.
Pi, drivers, I²C sensors and MOSFET board on the carrier; run deploy/install.sh.
Cells, dip tubes, check valves, reagent lines. Prime each pump from the dashboard.
pH buffers, Na₂CO₃ standard, two colorimetric standards each. Then let it run.