Sutro

Sutro is a smart pool water monitor that floats in the pool and automatically tests pH, free chlorine, and total alkalinity every hour using liquid reagent-based testing — the same chemistry used in professional DPD test kits. Founded in 2017 in San Francisco by Ravi Kurani, Sutro launched on Kickstarter and has grown into one of the leading connected pool monitoring brands.

Unlike ORP-based monitors (pHin, WaterGuru), Sutro uses actual liquid reagents dispensed from a replaceable cartridge, providing direct free chlorine measurements rather than ORP-derived estimates. The Sutro app calculates exact chemical doses based on pool volume, telling owners precisely how much of which chemical to add — down to the ounce. Sutro works with pools, hot tubs, and swim spas, and connects via WiFi to the Sutro cloud.

Sutro uses reagent-based testing — the same chemistry as a professional pool store test — providing direct free chlorine measurements rather than the ORP estimates used by competitors. The app calculates exact chemical doses by the ounce, not vague ranges. Automatic hourly testing catches chemistry swings before they cause algae blooms or equipment damage.

No calibration is needed — just replace the reagent cartridge every 90 days. Sutro works with chlorine, salt, bromine, and mineral sanitizer systems. The chemical dosing history in the app creates a log that helps identify patterns (e.g., chlorine drops every afternoon from UV, pH rises after adding salt).