How I Use Home Assistant for Reef Tank Monitoring and Safety

Fish tanks and Home Assistant are two of the best things in my house (after the people), so combining them was an obvious step. Like many reef keepers, I’ve looked at proper aquarium monitoring systems such as Apex. They’re impressive, but they’re also very expensive, and at their core they’re often little more than a smart power strip with a collection of sensors attached.

By pulling info from my reef tank into Home Assistant, I get a great view of what’s going on, alongside the rest of my home. More importantly, I can add automations that help protect the fish, corals and my home.

One of the leak sensors already paid for itself by alerting me early enough to fix a leak before it became damage.

Adding control of tank equipment into Home Assistant also makes day-to-day life easier. I can turn equipment on or off from my phone without crawling under the cabinet, unplugging things blindly, or trying to remember which plug does what.

This isn’t a step-by-step guide to fully automating a reef tank. Instead, it’s a practical look at how I use Home Assistant as a safety net and early warning system — reducing risk, catching problems early, and making day-to-day maintenance easier. In this post I’ll cover the handful of sensors and simple automations I use for temperature, heater safety, leak detection and ATO protection — plus why I’ve kept it simple.

My Approach to Reef Tank Automation

Before getting into the details, it’s worth broadly explaining how I approach automation with my reef tank.

Home Assistant is amazing and, in my experience, very reliable — but living things shouldn’t depend on it. Every critical piece of equipment on my tank is able to operate perfectly well on its own if Home Assistant goes offline.

Automation in my setup is a bonus, not a requirement. My setup is focused on monitoring and alerts, not full control.

When it’s easy to turn equipment off safely, see what’s running, or check the state of the tank at a glance, I’m simply more likely to do routine maintenance. Fewer awkward plugs to reach for and fewer “I’ll do it later” moments means jobs get done sooner and more consistently.

If Home Assistant stops working, the tank keeps running. If something starts behaving abnormally, Home Assistant helps me notice early — and makes it easier for me to act.

Most of my tank equipment is connected via a Meross smart multi-plug, giving me individual control over each piece of kit that keeps the tank running as well as a master switch to turn off all power to the tank. If you’re curious what hardware I’m using, I keep an updated list on my My Gear page.

This makes maintenance far easier and safer. I can shut things down cleanly from my phone without unplugging cables or risking mistakes.

It also opens the door to simple but useful automations, like maintenance modes or timed shutdowns.

What I monitor and What Happens When Something Looks Wrong

Risk\Problem	What I watch	What Happens
Tank too hot or cold	Temperature	Phone Notification
Heater behaving oddly	Heater runtime based on power draw	Phone notification
Leak under tank	Leak Sensor	High Priority phone alert + switch off ATO
ATO Pump running too long	ATO pump power draw	High Priority phone alert + switch off ATO
ATO reservoir running low	Distance sensor reading	Phone alert + switch off ATO

Temperature Monitoring With ESP32 + ESPHome (DS18B20)

Temperature is the single most important metric I monitor. For this, I use an ESP32 running ESPHome connected to a Dallas DS18B20 temperature sensor placed in the tank. Using automations, I get notifications on my phone if the tank gets too hot or too cold, combined with power monitoring I can quickly spot if the alert is caused by a problem with the heater.

Heater Safety: Detecting a Stuck-On Heater With Power Monitoring

Heater failure is one of the most common causes of catastrophes in fish tanks. When a heater gets stuck on the temperature can rise very quickly and cause issues within hours.

I use a power-monitoring smart plug on the entire tank. Instead of relying only on temperature, I also watch power draw. This allows me to see heater behavior. Because the heater is the biggest power draw on the tank I can clearly see heater cycles in the power graphs.

If the fish tank heater has been on for too long I get a notification on my phone. This extra monitoring and alerting lets me catch problems before they ruin the entire tank.

This gives me confidence that I’ll be alerted to abnormal behavior before temperature alone becomes dangerous.

Leak Detection (and Why It Already Paid for Itself)

Under my tanks I have leak sensors. They’re simple devices, but they’re arguably some of the most valuable sensors in my setup.

Recently, one of these sensors detected water and immediately sent an alert to my phone via the Home Assistant mobile app. I was able to investigate and fix a small leak quickly, before it caused any damage.

Without that alert, the leak could have escalated into a big problem.

ATO Protection: Preventing Run-Dry and Salinity Swings

Auto Top Off systems are convenient, but they can also cause real problems if something goes wrong. My new reef tank uses a gravity fed ATO with no plug so no monitoring is needed.

Previously, I used a distance sensor connected to an ESP32 running ESPHome to monitor the water level in the ATO reservoir. Using this information I knew when the reservoir needed refilling and Home Assistant would turn off the ATO automatically to make sure the pump didn’t run dry.
Using a power monitor on the ATO pump I could detect if it was running for too long. If the pump ran longer than expected, Home Assistant would cut power and alert me. If an ATO gets stuck on it can dump a whole container of water into the tank causing a salinity swing, upsetting corals and fish.

A Dedicated Reef Tank Dashboard in Home Assistant

I have a dedicated reef tank page on my dashboard in Home Assistant that brings everything together.

Having all of this visible at a glance — especially on mobile, makes it much easier to understand what’s happening with the tank without digging through individual devices and entities.

Lighting

Lighting is intentionally one of the simplest parts of my setup.

The tank lights are controlled by a Meross smart multi-plug, with schedules configured directly on the plugs rather than in Home Assistant. This reduces complexity and avoids another point of failure for something that needs to run reliably every day.

Looking ahead

I would like to add a camera feed of the tank into my home assistant dashboard. Partly just for fun but also so that I can check if everything looks normal when I’m away, some corals close up and tell me something is wrong before any sensor or automation can spot a problem.

While this may all sound very complicated each component is very simple.

As part of an ongoing tank move, I’m downsizing to a smaller all-in-one (AIO) tank, which I’ve already written about. Fewer components, less plumbing and less cables should reduce the number of things that can fail in the first place. I will still keep most of the stuff mentioned above because they will still help me keep a thriving healthy slice of the ocean in my front room. The goal is to keep the same monitoring philosophy, applied to a simpler smaller system.

If you’re already running Home Assistant, even a small amount of monitoring can make a big difference to the long-term stability of a reef tank. You don’t need to automate everything — just the right things.