Milwaukee Glass pH Probe - Hydros

The Milwaukee Glass pH Probe (MA991) is a gel-filled, glass-body electrode built to the standards of the laboratory and education markets. It pairs with any controller or standalone meter equipped with a BNC connector, including Hydros units, making it a practical replacement or upgrade option for reef keepers who want more consistent pH tracking. The glass sensing bulb and single Ag/AgCl reference junction deliver fast response times and stable readings across a 0–13 pH range, which more than covers the 7.8–8.5 window relevant to reef aquaria.

The probe's gel-filled interior and ceramic single-junction reference eliminate the need for liquid electrolyte top-offs, simplifying day-to-day maintenance. A spherical membrane geometry maximizes contact surface area, which contributes to quicker equilibration when moving between samples or during initial deployment. The BNC connector locks securely and resists corrosion in humid sump environments, and the 1-meter (3-foot) cable provides enough reach to route from a sump probe holder to a wall-mounted controller without an extension.

Longevity with any glass pH probe depends heavily on storage and calibration habits. The sensing bulb must be kept hydrated at all times — store the tip in pH storage solution or calibration buffer, never tap water or DI, and always keep the cap snug to prevent evaporation. The reference junction can clog if exposed to organic-rich water; periodic soaking in a dedicated electrode cleaning solution is the most effective way to maintain response speed and accuracy. Calibrate the probe regularly, and always re-calibrate after extended storage or cleaning cycles. With proper care, a glass probe at this quality level will provide reliable service for a meaningful period before sensitivity loss requires replacement.