Most reefers use a mix of digital colorimeters ("checkers", e.g., Hanna) and titration or color-card kits. Both can be accurate if used well; both can mislead if used carelessly.
How each works
| Type | How it reads | Strengths | Watch-outs |
|---|---|---|---|
| Hanna checker (e.g., HI772 alk, ULR phosphate/phosphorus) | Colorimetric absorbance | Numeric readout, low-range phosphate sensitivity | Cuvette cleanliness, bubbles, timing, reagent age |
| Titration kit (Salifert, Red Sea) | Count drops/mL to a color endpoint | Reliable for alk, Ca, Mg; low per-test cost | Endpoint judgment, syringe technique |
| Color-card kits | Match color to card | Cheap and quick | Hard to read at low nutrient levels |
Which should you use?
- Alkalinity: either; consistency matters most.
- Phosphate: a low-range checker is easier at 0.01–0.1 ppm.
- Magnesium/Calcium: titration kits are trusted standards for many reefers.
- Nitrate: low-range kits or checkers; avoid cards for SPS-level readings.
Validate your tests
Test freshly mixed salt at 35 ppt, compare two methods, or test a stored sample alongside an ICP. Product comparisons: test kit gear guide and best reef test kits.
FAQ
Why do my Hanna readings jump? Often fingerprints, bubbles or timing. Clean cuvettes and follow the timer.
Should I replace old reagents? Yes. Expired or heat-stored reagents drift.