Automated Water Changes (AWC) with Home Assistant

Manual water changes are the most tedious part of fishkeeping. An AWC (Automatic Water Change) system handles it for you — draining old water and replacing with fresh, dechlorinated water on a schedule. Home Assistant orchestrates the pumps, monitors water levels, and alerts you if anything goes wrong.

What You'll Need

Pumps & Valves

Dosing pump (Kamoer peristaltic) — moves water in/out
Float valve or optical sensor (AutoAqua Smart ATO) — detects water level
Solenoid valve (optional) — electrically controlled shutoff

Plumbing

PEX-B tubing (SharkBite 1/2") — flexible, durable water lines
SharkBite push-fit elbows — tool-free connections
SharkBite ball valve — manual shutoff for maintenance
Copper crimp rings + iCrimp tool — for permanent connections

Smart Controls

Tuya smart plugs — power the dosing pumps via HA schedule
Home Assistant — orchestrates the entire cycle

System Architecture

configuration.yaml

# AWC System Layout
#
# [Home Assistant]
#    |
#    ├── Tuya Plug 1 → Drain Pump → Tank → Waste Drain
#    |
#    ├── Tuya Plug 2 → Fill Pump → Reservoir → Tank
#    |
#    └── AutoAqua ATO → Float Sensor → Tank Water Level
#
# PEX plumbing connects reservoir, tank, and drain
# Float sensor triggers safety shutoff if overfill detected

Step 1: Plumbing the PEX Lines

Drain Line

Run 1/2" PEX from the tank to a floor drain or bucket
Use SharkBite push-fit elbows for corners
Install a SharkBite ball valve near the tank for manual shutoff

Fill Line

Run 1/2" PEX from a freshwater reservoir to the tank
The reservoir should be elevated above the tank or use a pump
Add a check valve to prevent backflow

Tools Needed

iCrimp PEX crimp tool — for permanent, leak-free connections
SharkBite copper crimp rings — secure PEX to fittings
PEX tubing cutter — clean cuts prevent leaks

Step 2: Set Up the Dosing Pumps

Drain Pump

Connect the Kamoer peristaltic pump to the drain PEX line
Plug into a Tuya smart plug
Calibrate: time how long it takes to pump 1 gallon

Fill Pump

Connect a second dosing pump (or gravity-feed from an elevated reservoir) to the fill PEX line
Plug into a separate Tuya smart plug
Calibrate: match the fill rate to the drain rate

configuration.yaml

# Entity IDs
switch.tuya_awc_drain_pump    # Drain pump power
switch.tuya_awc_fill_pump     # Fill pump power
binary_sensor.autoaqua_water_level  # Float/optical sensor

Step 3: AWC Automation — The Full Cycle

Weekly 20% Water Change

configuration.yaml

automation:
  - alias: "Weekly AWC — Drain Phase"
    description: "Drain 20% of tank water every Sunday at 2 AM"
    trigger:
      - platform: time
        at: "02:00:00"
    condition:
      - condition: time
        weekday:
          - sun
    action:
      - service: notify.mobile_app_your_phone
        data:
          message: "AWC starting — draining 20%..."
      # Turn on drain pump
      - service: switch.turn_on
        target:
          entity_id: switch.tuya_awc_drain_pump
      # Run for calculated time (e.g., 15 minutes for 15 gallons from a 75-gal tank)
      - delay:
          minutes: 15
      # Stop drain
      - service: switch.turn_off
        target:
          entity_id: switch.tuya_awc_drain_pump
      - delay:
          seconds: 30
      # Start fill
      - service: switch.turn_on
        target:
          entity_id: switch.tuya_awc_fill_pump
      # Run fill for same duration
      - delay:
          minutes: 15
      # Stop fill
      - service: switch.turn_off
        target:
          entity_id: switch.tuya_awc_fill_pump
      - service: notify.mobile_app_your_phone
        data:
          title: "AWC Complete"
          message: "Weekly water change finished. 20% replaced."

Safety Shutoff — Overfill Protection

configuration.yaml

automation:
  - alias: "AWC Safety — Overfill Shutoff"
    description: "Emergency stop if water level sensor detects overfill"
    trigger:
      - platform: state
        entity_id: binary_sensor.autoaqua_water_level
        to: "on"
    action:
      - service: switch.turn_off
        target:
          entity_id:
            - switch.tuya_awc_fill_pump
            - switch.tuya_awc_drain_pump
      - service: notify.mobile_app_your_phone
        data:
          title: "AWC EMERGENCY STOP"
          message: "Water level sensor triggered — all pumps stopped! Check the tank immediately."
          data:
            priority: high

Auto Top-Off (Evaporation Replacement)

Between water changes, evaporation drops the water level. The AutoAqua ATO handles this:

configuration.yaml

automation:
  - alias: "Auto Top-Off"
    description: "Top off evaporated water when level drops"
    trigger:
      - platform: state
        entity_id: binary_sensor.autoaqua_water_level
        to: "off"
        for:
          minutes: 5
    action:
      - service: switch.turn_on
        target:
          entity_id: switch.tuya_awc_fill_pump
      - wait_for_trigger:
          - platform: state
            entity_id: binary_sensor.autoaqua_water_level
            to: "on"
        timeout:
          minutes: 10
      - service: switch.turn_off
        target:
          entity_id: switch.tuya_awc_fill_pump

Step 4: Dashboard Card

configuration.yaml

type: vertical-stack
title: "Water Change System"
cards:
  - type: entities
    entities:
      - entity: switch.tuya_awc_drain_pump
        name: "Drain Pump"
        icon: mdi:water-minus
      - entity: switch.tuya_awc_fill_pump
        name: "Fill Pump"
        icon: mdi:water-plus
      - entity: binary_sensor.autoaqua_water_level
        name: "Water Level"
        icon: mdi:waves
  - type: button
    name: "Run AWC Now"
    icon: mdi:water-sync
    tap_action:
      action: call-service
      service: automation.trigger
      target:
        entity_id: automation.weekly_awc_drain_phase

My Setup

I run a Kamoer peristaltic pump on each line (drain + fill) controlled by Tuya smart plugs. The reservoir is a 32-gallon Brute trash can in the closet, pre-mixed with dechlorinator. PEX tubing runs through the wall — clean install, no visible hoses.

The AWC runs every Sunday at 2 AM. I calibrated the drain time by timing it with a 5-gallon bucket, then multiplied up. The AutoAqua ATO handles daily evaporation top-offs between changes.

The overfill safety shutoff has never triggered — but it's there for peace of mind. I tested it by manually triggering the float sensor.

Tips

Dechlorinate the reservoir water before it enters the tank — add Prime or similar to the reservoir when you fill it
Test connections before running — hand-fill the PEX lines and check every joint for drips
Calibrate pump timing carefully — run the drain into a bucket and time it before connecting to the tank
Install ball valves on both lines near the tank — lets you disconnect for maintenance without draining lines
Use a GFCI outlet for all pump power — water + electricity demands it

What's Next?

Salt Mixing Station — automated mixing for saltwater changes
Smart Power Management — monitor pump energy usage
Build Your Dashboard — the complete aquarium dashboard