Easier Aquarium Service with Automatic Water Changes using Dosing Pumps

Water changes in a marine aquarium system are one of the best things you can do to maintain balanced saltwater chemistry and simplify your aquarium service routine. In the previous article I described the measurement container method I used for several years. Here I will describe the calibrated dosing pumps method I am currently using on my 150-gallon display aquarium.

System Setup

The basic systems components of a dosing pump automatic saltwater exchange system include:

  • Saltwater mix and storage container
  • Mixing pump
  • Two volume-matched input and output dosing pumps
  • Controller with backup water level sensors
  • Tube plumbing
  • Drain access

The most critical aspect in any automatic saltwater exchange system is getting the new saltwater input precisely balanced with the old saltwater output. If they are not the same the water salinity will increase as too much saltwater is added, or the salinity will decrease as the freshwater top-off system replenishes removed saltwater. Dosing pumps, also called peristaltic pumps, have several advantages.

  • Strong suction to pull water (e.g. from 25 feet below the pump)
  • High head pressure to push water (e.g. to 60 feet above the pump)
  • Quality versions do not back siphon
  • Self-priming
  • Pump corrosive liquids (e.g. kalkwasser, vinegar, sodium hydroxide)

My dosing pump saltwater exchange system is shown in the diagram below. It was set up using the Spectrapure Liter Meter III (LM3), an external Water Exchange Module (WXM) plugged into the LM3, and an external Remote Pump Module (RPM) plugged into the LM3. The LM3 includes one pump and controls all three pumps. The LM3 pump, Pump A, moves water from the new seawater storage container to the sump. The WXM, Pump B, moves water from the sump to the quarantine tank. The WXM includes a pressure-activated level sensor. The sensor will turn the pump off if it is activated. The one on Pump B is used to sense the water level in the quarantine tank and turn the pump off if it gets to high, preventing it from overfilling. The RPM, Pump C, moves water from the quarantine tank to a utility sink in my garage and down the drain.  This last run is over 30 feet through the attic and down to the sink. Aquarium Service Automatic Water Change System

I set up the system to pump 6.4 liters per day (1.7 g/d). That is a little over 1 percent per day on my 150 gallon display plus sump aquarium system. The controller automatically turns on each pump in series for a short period of time many times each day.

Continuous Water Change Benefits

The efficiency of continuous water changes are essentially the same as individual large monthly water changes. Randy Holmes Farley described in his article Water Changes in Reef Aquaria that a continuous 30% water change per month (1% per day) is the same as a single 26% water change each month. There are also several advantages to continuous water changes.

  • The animals are not stressed with quickly changing water chemistry or temperature swings.
  • The saltwater storage mix tank does not need to be temperature matched to the display water. This saves the cost and bother of another heater.
  • The water in the sump does not go up and down. That allows for stable skimmer operation and unchanged level sensors such as the automatic freshwater top off sensor.
  • The aquarist is less likely to remember to do regular monthly manual water changes than setting up an automated continuous water change system once.

Saltwater Storage

My seawater storage mix tank is a 50-gallon plastic barrel. It has a float switch at the bottom to sense when the new water runs out. The sensor is connected to my Neptune Systems Apex aquarium controller. The aquarium controller powers the dosing pump controller. When the fresh saltwater runs out, the float switch activates, and the system controller turns off the pump controller. That way the saltwater does not continue to be pumped out of the sump.

Quarantine Tank

Normally only two pumps are needed for a water change. I added a 10 gallon Quarantine Tank (QT) and third pump to provide several advantages to the quarantine system.

  • Relatively clean and chemically balanced display tank water is continuously run through the quarantine system.
  • Large automatic water changes (in my case 17% per day or 510% per month) eliminate the need for QT water testing, service and adjustments.
  • Animals in quarantine become familiar with their ultimate destination’s water chemistry. This allows for no acclamation and little stress when moved.
  • The QT is always perfectly ready for those impulse buys. Just keep the heater on.

This one-way water flow from main system to quarantine system to drain isolates the main system from any parasites or diseases in the quarantine system. I still use a hang on the back filter as a backup and for water flow.

New Saltwater

I am fortunate to live where I can get free natural sand-filtered seawater. I normally do not need to mix up synthetic saltwater, but I still periodically use it. Whenever there is a rainstorm the natural seawater phosphate level will spike from storm drain runoff and I avoid using it. I equipped the new seawater storage barrel with additional equipment to semi automate new synthetic saltwater mixing. I start by manually turning off the dosing pump controller. I then open a ¼ tube valve from my RO/DI water filter. This puts water directly into the storage barrel. When the barrel is full, a mechanically actuated float valve at the top of the barrel automatically stops the input. Once full, I close the valve, add about 15 pounds of salt, and turn on a mixing power head installed in the barrel. Once it has mixed for a day, I turn the dosing controller back on.

As mentioned above I do not need to use a heater in the mixing storage container. Such small volumes are dosed into the sump that there is no chance of temperature-shocking the animals.


Automatic water changes using dosing pumps provide several advantages to the aquarist of which the most important is that this key aquarium service step will get done on a regular basis.  Setting up an automatic water change system will eliminate one of the most dreaded aquarium service tasks and make your aquarium more enjoyable. I hope this example on my system will help you enjoy your aquarium more.

Happy marine aquarium servicing.

One Response to Easier Aquarium Service with Automatic Water Changes using Dosing Pumps

  1. noel August 12, 2014 at 3:18 am #

    awesome! thanks for sharing … i am hoping i could do this in the near future

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