Ohaus Starter ST20
#7 in Pen testersFull review
A pen tester from a lab-balance maker, for classrooms and labs buying Ohaus gear. The Apera PH60 is more accurate for less.
Amazon $104.62$104.62
The Ohaus Starter ST20 is the better ph meter overall, rated 3.3 to 2.7. The Ohaus Starter ST20 leads on features, accuracy and calibration. The Bluelab pH Pen costs $14.67 less ($89.95 vs $104.62).
Prices were last checked November 9, 2026. Product prices and availability are accurate as of that date and are subject to change; the price and availability shown on Amazon or the retailer's site at the time of purchase apply. As an Amazon Associate we earn from qualifying purchases.
Bluelab pH Pen
#13 in Pen testersFull review
A simple, tough pen for growers checking nutrient pH. The PenPlus costs a little more and adds a replaceable probe.
Amazon $89.95$89.95
Which should you buy?
- Choose the Ohaus Starter ST20 for features (replaceable probe, automatic temperature compensation, waterproof (IP67) vs automatic temperature compensation, waterproof), accuracy (±0.05 pH vs ±0.1 pH) and calibration (3-point calibration vs 2-point calibration).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every pen testers ph meter; a clear win is highlighted. How we rank explains each one.
| Factor weight | Ohaus Starter ST20 | Bluelab pH Pen |
|---|---|---|
| Overall rating | 3.3/5 | 2.7/5 |
| Accuracy 30% | 38 ±0.05 pH | 19 ±0.1 pH |
| Calibration 15% | 85 3-point calibration | 50 2-point calibration |
| Features 20% | 80 replaceable probe, automatic temperature compensation, waterproof (IP67) | 40 automatic temperature compensation, waterproof |
| Extra readings 10% | 0 pH and temperature only | 0 pH and temperature only |
| Price 15% | 76 $104.62 | 82 $89.95 |
| Warranty 10% | 0 warranty not published, scored as none | 0 1-year meter warranty |
Specifications
| Ohaus Starter ST20 | Bluelab pH Pen | |
|---|---|---|
| pH measurement | ||
| Accuracy | ±0.05 pH | ±0.1 pH |
| Resolution | 0.01 pH | 0.1 pH |
| Range | 0 to 14 pH | 0 to 14 pH |
| Calibration | 3-point | 2-point |
| Temperature compensation | Yes | Yes |
| Other readings | ||
| Conductivity (EC/TDS) | No | No |
| ORP | No | No |
| Salinity | No | No |
| Build | ||
| Replaceable probe | Yes | No |
| Waterproof rating | IP67 | Waterproof |
| Battery life | 200 hours | - |
| Weight | 110 g | - |
| Meter warranty | - | 1 year |