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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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jerry says...
Hi, Glass reef, i like your set up and the idea of not having to do water change. I want to do the same with my tank, could you please let me know where i can purchase this liter meter 3 in australia, as the people that sells them in the US don't ship to Australia, thanks, i shall wait for your reply, kind regards, jerry
15th February 2013 10:26pm
Dave says...
I have my holding tanks in the basement. I would have to move water 30' and up one level, would this work?
13th April 2012 8:07am
Kevin says...
Any reason you don't just flush the fresh water tank contents into the salt water holding tank to avoid the 9 hour wait to produce RO water?
GlassReef: Good question. I have my fresh water ATO (sump) refill set so that a 1/4" drop in water level causes the ATO's fill motor to start. The result is a "fill cycle" of about 45 minutes. This means that there must always be a sufficient level of RO water in the fresh water tank. Though it would probably be possible to move the RO water to the saltwater tank, I decided not to do so that the ATO cycle is never disturbed. The automated saltwater change process I use is only affected for a short time. I doubt if the inhabitants in the tank even notice it.the tank
2nd January 2012 6:16pm
Joey says...
Cool site!!

Would the LiterMeter Water eXchange module do the same, as the LiterMeter Remote pump module, which you have?

I have the Litemeter III , and was thinking of implementing the same setup but with the eXchange module.


GlassReef: Good morning! The LiterMeter exchange module is a remote module plus a water level controller which shuts down the remote pump when the water level reaches a desired depth. In my opinion, the water level controller isn't needed for a continuous water change setup. The accuracy of the old water removal and addition of new water is dependent upon calibrating two pumps that work together to ensure that the quantities of water out and water in are the same. A means of level control plays no role in the process. An automated top-off unit (with max/min float switches, for example) would handle that.
10th May 2011 4:09am

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