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
±0.05 pH3-pointNone
3.1/5
A cheap, waterproof pen for pools, aquariums and drinking water. Pick it when 0.1 pH is close enough.
- ±0.1 pHAccuracy
- 3-pointCalibration
- IP67Waterproof
- NoReplaceable probe
Check price at Amazon$56.65
Price checked November 8, 2026. As an Amazon Associate we earn from qualifying purchases.
Pros
- Cheapest pen here that still calibrates at up to three points
- IP67 housing floats if it is dropped in a tank or pool
- Up to 2,000 hours on a set of AAA batteries
Cons
- Reads to 0.1 pH only, too coarse for brewing or lab work
- Probe is built in, so a worn sensor means a new tester
How it scores
The rating comes from 6 measured or published factors, each scored 0-100 against fixed reference points for its type. How we rank explains each one.
Specifications
| Model number | AI209 |
|---|---|
| pH measurement | |
| Accuracy | ±0.1 pH |
| Resolution | 0.1 pH |
| Range | 0 to 14 pH |
| Calibration | 3-point |
| Temperature compensation | Yes |
| Other readings | |
| Conductivity (EC/TDS) | No |
| ORP | No |
| Salinity | No |
| Build | |
| Replaceable probe | No |
| Waterproof rating | IP67 |
| Battery life | 2,000 hours |
| Weight | 107 g |
| Meter warranty | 2 years |
| Probe warranty | 6 months |
Alternatives in this type
Milwaukee pH58 Max pH/ORP
#8 in Pen testersFull review
A pen for pool and water-treatment work that needs ORP as well as pH. For pH alone, cheaper pens are as accurate.
Amazon $219.65$219.65
±0.05 pH2-pointORP
Hanna pHep 5 HI98128
#10 in Pen testersFull review
A well-made pocket tester from a lab brand, for anyone who already uses Hanna buffers and electrodes. The Apera PH60 does more for less.
Amazon $179.99$179.99
±0.05 pH3-pointNone
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