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         Implementing An Automated Water Change System

Most saltwater aquarists agree that regular water changes - new water exchanged for old - are necessary to maintain a healthy system.  The majority of water changes are done in bulk - that is, a percentage of a systems water volume is change all at once. A common goal is to exchange 7% to 10% of a tank's water every week. With my system, which has a total volume of more than 530 gallons, that means mixing 53 gallons of saltwater, removing 53 gallons of old water from the system, and then replacing the old with the new. I can tell you, from experience, such a water change can be a challenge. You need containers for the old and new water, hoses, pumps, etc.

In order to simplify the whole water change scenario, I decided to implement an automated system. Not only did I want to make it automated, I wanted it to be a continual process. The water should be constantly in the process of being changed. If I stick to the 10% per week formula, I would have to change approx. 7.6 gallons per day, or about .32 gallons an hour. Luckily, this is easily accomplished with peristaltic (dosing) pumps. The firm Spectrapure manufactures the perfect pump - their LiterMeter III. The LiterMeter comes in two variants.

1. a control module which integrates a pump with a computer:

LiterMeter-III closeup

2. a remote module which has no built-in controller. It can be attached to the control module, as shown below, and makes use of it's control capabilities:

The dosing pumps are located on a shelf, just above my 65 gallon saltwater storage tank:

One pump draws fresh saltwater from the reservoir and moves it to the return section of the sump. The other pump draws old water from the overflow section of the sump and moves it to the drain located below my utility sink. This happens 150 times every 24 hours - the LiterMeter divides it's daily amount to pump into 150 equal intervals.

Utilizing the dosing pumps and the storage tank, the water change process becomes very simple. Once every 10 days, or so, (when the saltwater storage tank is empty) I set the LiterMeter to OFF, and turn a valve allowing RO/DI water to trickle into the tank. The water stops when a float valve is activated - takes about 9 hours as I have a double 75gal cartridge RO - at that point I turn the RO valve to the off position. Then I dump in a 55gal bag of salt (there's always 10gal left in the tank when I start filling) and turn on a circulation pump to mix the water. I let it run until I feel like turning it off. After the water's mixed, I set the LiterMeter to RUN. The system changes about 7.6 gallons each 24 hours.

So all that's required for continual water changes is - every 8th day:

  • set the LiterMeter to OFF
  • turn a valve ON
  • turn a valve OFF
  • dump in a bag of salt
  • turn on a pump
  • turn off a pump
  • set the LiterMeter to RUN

That's it - the whole thing (other than RO fill time) takes less than 5 minutes.

The beauty of doing changes this way is that because of the small amount of water being removed or added at any given time:

  •  the temperature of the new water is not a concern - too little is being added at any given time to cause a change

  • specific gravity is normally never affected. If it changes, due to too much or too little salt in the mixing tank, the change will be very gradual (1.026 > 1.025 for example) over a period of days - this can be very easily and safely corrected

  • changing the brand of salt used is not a concern. As an example, I've been using Tropic Marin Pro for quite a while. Correctly mixed up to an SG of 1.026 it has an alkalinity of 8.2 dKH. I mention this, as I will soon be changing to Instant Ocean salt (see my reef blog of 7/01/2010 for the reason why), which has an alkalinity of approx. 11 dKH. This difference in alkalinity will not constitute a problem at all, because of the small amount of water being exchanged each day.

All in all, I've found that this method makes for very stable temperature and specific gravity conditions.

BTW - Some may wonder about the efficiency of doing continual water changes. "Aren't you immediately changing out some of the NEW water with the OLD"? Let me quote a small part of a Reefkeeper Magazine (RKM) article from Randy Holmes-Farley:

"These changes are slightly less efficient than single batch water changes of the same total volume. A continuous water change of 30% exactly matches one batch 26% water change. As with very small batch water changes, these have the advantage of neither stressing the organisms (assuming the change is done reasonably slowly), nor altering the water level in the aquarium. The ease of doing such changes automatically also makes it far more likely that busy or lazy aquarists will actually do them."

For those interested, here's a link to the full article: Water Changes In Reef Aquaria



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geck31 says...
didn't you have the Masterflex Peristaltic Pump? what happened was it a case of out with the old and in with the new?
26th May 2015 12:07am
Jim Ryan says...
Is there a safety in the system so that if one pump fails the system will shut down?
GlassReef: There is no automated safety system involved. I display the current pH of the tank's water, both on the wall on the viewing side of the tank and on my computer's desktop. Any change in pH will result in my checking for the cause. This will always include the correct functioning of the water change system. The system, itself, makes use of check valves, float valves, etc. to ensure that uncontrolled flow is not possible.
11th February 2015 1:21pm
Travis says...
Could the same activity be done with the Bubble magus dosing pump system?
GlassReef: Calculate the max flow you can attain in a week with your magnus. If it equals, at least, 2% of you the total water in your system, your fine.
17th September 2014 2:07pm
Jim Ryan says...
I know your post is 3 years old so I am not sure if you still monitor it. If you do can you tell me how your system has held up over time. Also do the two pumps pump exactly as much as each other? What would happen if one of the pumps broke or went out of calibration and is there a safety to shut the system down if this happens? I travel lots and only make it home for short periods every couple of weeks in the summer and my tank suffers for it. The other side is I can't have something that would keep pumping water in if the pump removing water shut down. Thanks
6th May 2014 6:49pm
Scott says...
I have my Rodi system in my basement and currently haul water from there up stairs to my tank. Would these dosing pumps push that water up 8-10 feet through a 30-35 foot line? If so "I'm in" if not, can you recommend a better pump?
GlassReef: Hi Scott, The LiterMeter III has a draw height (pump upstairs - pulling up) of 12 feet or a delivery height (pump downstairs - pushing up) of 60 feet. Would be fine for your needs.
30th March 2013 8:59pm
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