Bluelab OnePen
#6 in Pen testersFull review
A connected pen for serious hydroponic growers who want pH and nutrient readings logged to their phone. Most buyers get more for less from the Apera PC60.
Amazon $249$249
±0.05 pH2-pointEC/TDS
3.2/5
A pen for pool and water-treatment work that needs ORP as well as pH. For pH alone, cheaper pens are as accurate.
- ±0.05 pHAccuracy
- 2-pointCalibration
- WaterproofWaterproof
- YesReplaceable probe
Check price at Amazon$219.65
Price checked November 8, 2026. As an Amazon Associate we earn from qualifying purchases.
Pros
- Reads ORP as well as pH, useful for pool and spa sanitizer checks
- Replaceable electrode
Cons
- Pricey for a pen with two-point calibration
- About 250 hours per set of batteries
The Milwaukee waterproof testers family
Every Milwaukee waterproof testers model we rank, smallest first. Ratings compare each against its own type.
| Model | Accuracy | Rating | Price |
|---|---|---|---|
| Milwaukee pH55 Pro | ±0.1 pH | 3.0/5 | $77.90 |
| Milwaukee pH58 Max pH/ORP (this one) | ±0.05 pH | 3.2/5 | $219.65 |
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 | pH58 |
|---|---|
| pH measurement | |
| Accuracy | ±0.05 pH |
| Resolution | 0.01 pH |
| Range | -2 to 16 pH |
| Calibration | 2-point |
| Temperature compensation | Yes |
| Other readings | |
| Conductivity (EC/TDS) | No |
| ORP | Yes |
| Salinity | No |
| Build | |
| Replaceable probe | Yes |
| Waterproof rating | Waterproof |
| Battery life | 250 hours |
| Weight | 99 g |
| Meter warranty | 2 years |
| Probe warranty | 6 months |
Alternatives in this type
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
Apera PH20
#9 in Pen testersFull review
A cheap, waterproof pen for pools, aquariums and drinking water. Pick it when 0.1 pH is close enough.
Amazon $56.65$56.65
±0.1 pH3-pointNone
Compare
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