Fish-o-mat: An Aquaponics Greenhouse Controlled by ESPHome and Home Assistant

The Problem

Aquaponics combines fish farming and plant cultivation in one water cycle: the fish produce nutrients, bacteria convert them, and the plants clean the water that flows back to the fish. In my greenhouse two separate systems – a left and a right side – are running, each with its own fish tank, grow bed and vertical pipe towers for lettuce. The fish are catfish.

Such a system only works if a handful of things run reliably, day and night, all year round:

• the water pump has to keep the water circulating,
• the air pump has to keep enough oxygen in the water,
• the water temperature has to stay in a narrow range – in winter the greenhouse gets cold, in summer it gets hot,
• and the fish have to be fed regularly and in the right amount.

Commercial controllers are either expensive, cloud-bound or impossible to integrate into an existing home automation. I wanted a solution that runs locally, uses cheap standard components, alerts me when something goes wrong and integrates into my Home Assistant installation – and ideally heats the water with solar surplus instead of grid power.

The Solution

The picture shows the greenhouse shortly after the setup – the pipe towers are still waiting for their plants. It holds two identical systems. On the back wall a board carries the air pumps, the power distribution, an energy meter and the two controller boxes. Above each fish tank sits a 3D-printed automatic fish feeder; the lettuce grows in the gravel beds on top of the tanks and in the vertical pipe towers on both sides.

The controller: Fish-o-mat

Each side has its own Fish-o-mat – a controller box built around an ESP32 running ESPHome. Each box contains:

• an ESP32-D1 mini connected via WiFi
• a 4-channel relay module with four potential-free contacts (230 V / 10 A each) for heating, cooling, air pump and water pump
• a 1-Wire bus (VCC, DQ, GND) for the temperature sensors – air temperature and substrate/water temperature
• a 5 V USB power supply for the electronics and terminals for the 230 V supply

All mechanical parts are designed by myself and produced with the tools of smart production: the mounting plate is laser-cut from plywood with all connections engraved directly on it (“USB Netzteil (5V)”, “4x Potentialfreie Kontakte zu je 230V/10A”, the reset button …), so maintenance is easy even years later. The fish feeders are 3D printed (model on MakerWorld, firmware on GitHub). Everything sits in standard IP-rated junction boxes.

Caution: These boxes switch mains voltage. Work on 230 V installations must only be carried out by qualified persons.

Firmware

The firmware is a plain ESPHome configuration: the temperature sensors and the four relays are declared in a few lines of YAML, and ESPHome makes them available to Home Assistant via its native API – no MQTT broker or custom code required. The control logic itself (thermostat, timers, PV surplus) lives in Home Assistant.

Home Assistant

The dashboard mirrors the physical layout: the left system on the left, the right system on the right, shared information in the middle.

• Per side: air and substrate temperature, the state of heating, cooling, air pump and water pump, and a thermostat that keeps the water between 25 and 27 °C. Light, feed now and clear jam are available as buttons.
• PV surplus heating: a switch per tank lets the heating run on solar surplus, so the water is warmed with energy that would otherwise be fed into the grid.
• Energy: the greenhouse power supply can be switched centrally; current power and total energy consumption are measured.
• Stock information: from the total fish weight Home Assistant calculates the average weight, the daily growth and the required amount of food per day (feeding rate 3.5 % of the body weight).
• Feeding: the automatic feeding can be switched on and off; a chart shows the weight of both food reservoirs, so you can see at a glance whether each feeding actually happened.
• Camera: a live view of the greenhouse.

The result

The fish supply the fertilizer, the system does the rest: in summer basil fills the pipe towers, and tomatoes and cucumbers grow up to the roof of the greenhouse.

And of course the fish are part of the harvest as well:

Conclusion

After one full season (March to November) these are my take-aways:

• Heating is a must in spring and autumn. From March to April and again from September the water has to be heated. That added up to about 2 MWh of electricity – all of it solar power from my own PV system, which is exactly why the PV surplus switch exists.
• Cooling is a must in summer. On sunny days the greenhouse reaches peaks of more than 50 °C.
• Zero tolerance for errors. Plants and fish are living beings: a pump that stops or a heater that gets stuck can wipe out a whole season. Reliable hardware and alerts are not optional.
• About one hour of work per week, averaged over the season: measuring water parameters, cleaning filters, harvesting and cleaning up.
• Growth is exponential – and so is the cleaning effort. The upside: the fertilizer gain grows as well, and the garden is grateful.

The numbers of one season

Building the system was a one-time effort of about 200 hours for the greenhouse including the foundation and about 100 hours for planning and developing the concept – including roughly 40 hours for building and testing the fish feeder, 20 hours for the ebb-and-flow siphon and 10 hours for the solids filter.

Doing it yourself is the key to cost efficiency – and building it is half the fun.