Local aquarium monitoring with Home Assistant

Aquarium monitoring needs precise, real-time water data: temperature, pH, ORP, salinity, and dissolved oxygen. Here’s the honest part most “smart home” articles skip — there are no off-the-shelf Zigbee or Z-Wave pH or ammonia sensors. Companies like Third Reality make Zigbee temperature/humidity, leak, and soil-moisture sensors, but no pH or ammonia probe. Water chemistry sensing is an analog, wet-chemistry problem, so the real local-first answer is a DIY ESPHome build with proper aquarium probes wired to an ESP32. This guide reframes the project around what actually exists.

The right architecture: ESP32 + ESPHome + analog probes

The proven approach is an ESP32 running ESPHome, reading water-quality probes, and reporting entities to Home Assistant over your LAN with no cloud. The well-known open-source example is the AquaPi project, which builds exactly this on ESPHome.

Sensor choices that actually exist:

• Temperature: a waterproof DS18B20 probe (1-Wire). Cheap, stable, accurate to roughly ±0.5 °C, and natively supported in ESPHome.
• pH: the DFRobot Gravity Analog pH V2 (~$30, read on an analog ADC pin after two-point calibration) or the Atlas Scientific EZO-pH circuit (~$60, with temperature compensation and better noise rejection).
• ORP / salinity / dissolved oxygen: Atlas Scientific EZO circuits cover these. They communicate over I²C or UART, both readable from an ESP32 in ESPHome.

Wire probes into a sealed enclosure with cable glands, give the ESP32 a stable power supply, and calibrate each probe on a schedule — analog probes drift and need periodic recalibration.

Integrate into Home Assistant

Because the device runs ESPHome, Home Assistant discovers it automatically over the local network. Each probe becomes a sensor entity (temperature, pH, ORP, etc.) with native history and graphing. No cloud account, no vendor app.

From there, build automations locally:

• Alert (local push notification or a TTS announcement on a local speaker) if temperature leaves a safe band.
• Alert if pH drifts outside your target range for the tank’s livestock.
• Drive a smart plug (a Zigbee or Z-Wave plug, or an ESPHome relay) to switch a heater, chiller, dosing pump, or CO2 solenoid based on readings.

Keep control logic in Home Assistant or directly on the ESP32 so the tank stays managed even if HA restarts.

Leak protection and water control

A tank monitor should include leak and overflow protection:

• A Zigbee water-leak sensor (e.g. Third Reality or Aqara, via your own Zigbee coordinator) on the floor near the stand and sump.
• An automatic shutoff — a motorized water valve (for example a SwitchBot valve, or a Z-Wave/Zigbee valve) triggered by the leak sensor — to stop a top-off or auto-water-change line.

These are genuine products and integrate locally, unlike the imaginary “pH/ammonia Zigbee sensors.”

Redundancy and power

Aquariums are unforgiving of downtime. Put the ESP32, the Home Assistant host, and critical pumps on a UPS so a brief outage doesn’t crash the system. Run Home Assistant on reliable local hardware (a dedicated mini PC or a Raspberry Pi with good power and storage). Consider a second independent temperature alarm as a hardware backstop for the most critical parameter.

Related products

Local-first picks from our catalog that fit this topic:

• Athom Smart Plug V2 (ESPHome) - plug
• Shelly Plus Plug US - plug
• Tesla Wall Connector (Gen 3) - ev-charging
• Amcrest AD410 Video Doorbell - camera

Quick verdict

Local aquarium monitoring with Home Assistant is very achievable — but the honest path is DIY ESPHome on an ESP32 with real analog probes (DS18B20 for temperature, DFRobot or Atlas Scientific EZO for pH/ORP/DO), not nonexistent Zigbee chemistry sensors. Add a Zigbee leak sensor and an automatic shutoff valve for safety, keep everything on a UPS, and you get a transparent, subscription-free monitor you fully own.