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
The Bluelab OnePen is the better ph meter overall, rated 3.4 to 3.2. The Bluelab OnePen leads on features. The Milwaukee pH58 Max pH/ORP costs $29.35 less ($219.65 vs $249).
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.
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
Which should you buy?
- Choose the Bluelab OnePen for features (replaceable probe, automatic temperature compensation, waterproof (IP68), stores readings vs replaceable probe, automatic temperature compensation, waterproof).
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 | Bluelab OnePen | Milwaukee pH58 Max pH/ORP |
|---|---|---|
| Overall rating | 3.4/5 | 3.2/5 |
| Accuracy 30% | 38 ±0.05 pH | 38 ±0.05 pH |
| Calibration 15% | 50 2-point calibration | 50 2-point calibration |
| Features 20% | 100 replaceable probe, automatic temperature compensation, waterproof (IP68), stores readings | 70 replaceable probe, automatic temperature compensation, waterproof |
| Extra readings 10% | 70 conductivity (EC/TDS) | 70 ORP |
| Price 15% | 38 $249 | 44 $219.65 |
| Warranty 10% | 25 2-year meter warranty | 25 2-year meter warranty |
Specifications
| Bluelab OnePen | Milwaukee pH58 Max pH/ORP | |
|---|---|---|
| pH measurement | ||
| Accuracy | ±0.05 pH | ±0.05 pH |
| Resolution | 0.01 pH | 0.01 pH |
| Range | 0 to 14 pH | -2 to 16 pH |
| Calibration | 2-point | 2-point |
| Temperature compensation | Yes | Yes |
| Other readings | ||
| Conductivity (EC/TDS) | Yes | No |
| ORP | No | Yes |
| Salinity | No | No |
| Build | ||
| Replaceable probe | Yes | Yes |
| Waterproof rating | IP68 | Waterproof |
| Connectivity | Bluetooth app | - |
| Battery life | - | 250 hours |
| Weight | - | 99 g |
| Meter warranty | 2 years | 2 years |
| Probe warranty | 6 months | 6 months |