Automated Salt Mixing Station for Saltwater Tanks

Saltwater aquariums need consistent salinity. A mixing station pre-mixes salt water to the right concentration and temperature before it enters the tank. Home Assistant automates the mixing schedule, matches temperature, and controls dosing pumps — so your water changes are always consistent.

What You'll Need

Mixing container — food-safe bucket or Brute trash can (20-50 gallons)
Powerhead/circulation pump — mixes salt into the water
Submersible heater — temperature-matches the new water to the tank
Dosing pump (Kamoer peristaltic) — pumps mixed water to the tank
Salt mix (Instant Ocean or Reef Crystals)
Refractometer — measures salinity (manual check)
Tuya smart plugs — control the powerhead, heater, and dosing pump
Inkbird temperature controller — matches reservoir temp to tank temp
Home Assistant — orchestrates everything

System Architecture

configuration.yaml

# Salt Mixing Station Layout
#
# [Mixing Container]
#   ├── Powerhead (Tuya plug) → Circulation/mixing
#   ├── Heater (Inkbird) → Temperature matching
#   └── Dosing Pump (Tuya plug) → Delivers to tank
#
# [Home Assistant]
#   ├── Schedule: Start mixing 24h before water change
#   ├── Monitor: Temperature matching (Inkbird sensor)
#   └── Execute: Pump mixed water to tank when ready

Step 1: Physical Setup

Place the mixing container near the tank (closet, cabinet, or utility area)
Fill with RO/DI or dechlorinated fresh water
Add salt mix per manufacturer instructions (typically 1/2 cup per gallon for 1.025 SG)
Drop in the powerhead — it circulates and dissolves the salt
Add the submersible heater — set to match your tank temperature
Connect the dosing pump output to PEX tubing running to the tank

Step 2: Smart Plug Configuration

configuration.yaml

# Entity IDs for the mixing station
switch.tuya_salt_powerhead      # Circulation pump
switch.tuya_salt_heater         # Or Inkbird-controlled heater
switch.tuya_salt_dosing_pump    # Delivers water to tank
sensor.inkbird_salt_temperature # Reservoir water temp
sensor.inkbird_tank_temperature # Tank water temp (for matching)

Step 3: Automated Mixing Schedule

Start mixing 24 hours before your scheduled water change to allow full dissolution and temperature matching:

configuration.yaml

automation:
  - alias: "Salt Mix — Start Mixing"
    description: "Start powerhead and heater 24 hours before water change"
    trigger:
      - platform: time
        at: "02:00:00"
    condition:
      - condition: time
        weekday:
          - sat
    action:
      - service: switch.turn_on
        target:
          entity_id:
            - switch.tuya_salt_powerhead
            - switch.tuya_salt_heater
      - service: notify.mobile_app_your_phone
        data:
          message: "Salt mixing started. Will be ready for Sunday AWC."

  - alias: "Salt Mix — Ready Notification"
    description: "Notify when reservoir temp matches tank temp (ready to use)"
    trigger:
      - platform: template
        value_template: >
          {{ (states('sensor.inkbird_salt_temperature') | float -
              states('sensor.inkbird_tank_temperature') | float) | abs < 1 }}
    condition:
      - condition: state
        entity_id: switch.tuya_salt_powerhead
        state: "on"
    action:
      - service: notify.mobile_app_your_phone
        data:
          title: "Salt Water Ready"
          message: "Reservoir is {{ states('sensor.inkbird_salt_temperature') }}°F — within 1°F of tank. Ready for water change. Check salinity with refractometer."

Step 4: Integration with AWC

After the salt water is mixed and temp-matched, integrate with your AWC automation:

configuration.yaml

automation:
  - alias: "Saltwater AWC — Full Cycle"
    description: "Drain old water, pump in mixed salt water, shut down station"
    trigger:
      - platform: time
        at: "02:00:00"
    condition:
      - condition: time
        weekday:
          - sun
      # Only run if mixing station has been running (water is ready)
      - condition: state
        entity_id: switch.tuya_salt_powerhead
        state: "on"
    action:
      # Phase 1: Drain
      - service: switch.turn_on
        target:
          entity_id: switch.tuya_awc_drain_pump
      - delay:
          minutes: 15
      - service: switch.turn_off
        target:
          entity_id: switch.tuya_awc_drain_pump
      - delay:
          seconds: 30
      # Phase 2: Fill with mixed salt water
      - service: switch.turn_on
        target:
          entity_id: switch.tuya_salt_dosing_pump
      - delay:
          minutes: 15
      - service: switch.turn_off
        target:
          entity_id: switch.tuya_salt_dosing_pump
      # Phase 3: Shut down mixing station
      - service: switch.turn_off
        target:
          entity_id:
            - switch.tuya_salt_powerhead
            - switch.tuya_salt_heater
      - service: notify.mobile_app_your_phone
        data:
          title: "Saltwater AWC Complete"
          message: "Water change done. Mixing station shut down. Refill reservoir when convenient."

Step 5: Salinity Monitoring

Currently, salinity requires a manual refractometer reading. Log it in Home Assistant with an input number:

configuration.yaml

input_number:
  salt_tank_salinity:
    name: "Tank Salinity (SG)"
    min: 1.000
    max: 1.040
    step: 0.001
    unit_of_measurement: "SG"
    icon: mdi:water-percent

  salt_reservoir_salinity:
    name: "Reservoir Salinity (SG)"
    min: 1.000
    max: 1.040
    step: 0.001
    unit_of_measurement: "SG"
    icon: mdi:water-percent

Add a salinity alert if it drifts:

configuration.yaml

automation:
  - alias: "Salinity Drift Alert"
    description: "Alert if tank salinity is outside 1.024-1.026 range"
    trigger:
      - platform: numeric_state
        entity_id: input_number.salt_tank_salinity
        above: 1.026
      - platform: numeric_state
        entity_id: input_number.salt_tank_salinity
        below: 1.024
    action:
      - service: notify.mobile_app_your_phone
        data:
          title: "Salinity Alert"
          message: "Tank salinity is {{ states('input_number.salt_tank_salinity') }} SG — outside safe range (1.024-1.026)"

Step 6: Dashboard Card

configuration.yaml

type: vertical-stack
title: "Salt Mixing Station"
cards:
  - type: entities
    entities:
      - entity: switch.tuya_salt_powerhead
        name: "Powerhead"
        icon: mdi:fan
      - entity: switch.tuya_salt_heater
        name: "Heater"
        icon: mdi:fire
      - entity: sensor.inkbird_salt_temperature
        name: "Reservoir Temp"
        icon: mdi:thermometer
      - entity: input_number.salt_reservoir_salinity
        name: "Reservoir Salinity"
      - entity: input_number.salt_tank_salinity
        name: "Tank Salinity"
  - type: gauge
    entity: input_number.salt_tank_salinity
    name: "Tank Salinity"
    min: 1.020
    max: 1.030
    severity:
      green: 1.024
      yellow: 1.022
      red: 1.020

My Setup

I use a 32-gallon Brute trash can in a closet as my mixing reservoir. A small powerhead mixes the salt, and an Inkbird-controlled heater matches the temperature to the tank. Saturday morning the mixing station turns on; Sunday at 2 AM the AWC cycle runs. After the water change, the mixing station shuts itself off.

I manually check salinity with a refractometer before each water change and log it in the HA dashboard. One day I'll add an inline salinity sensor, but the manual check takes 30 seconds and keeps me engaged with the tank.

Tips

Mix for at least 24 hours — gives salt time to fully dissolve and stabilize
Temperature match within 1°F — sudden temp changes stress corals and fish
Use RO/DI water for mixing — tap water introduces phosphates and silicates
Keep the container covered — prevents evaporation and contamination
Refill the reservoir right after a water change while you remember

What's Next?

Automated Water Changes — the full AWC system guide
Temperature Monitoring — Inkbird setup + alerts
Build Your Dashboard — the complete aquarium dashboard