Saltwater Fish Tank Water Change System

Posted in Projects by Bill
17 Jan 2010

Not all my projects are robotic in nature. This one, a simple water change system for our 40 gallon saltwater tank, is one of those non-robotic projects. For those who are unfamiliar with fish tanks, about once a week you have to change out roughly 10% of the water. The way we have been doing water changes involved two trips to the toilet with a mob bucket, and a lot of mixing of water in the shower. I decided to build a better way.

The system consists of a valve manifold inline with the tank’s filtration system, a bilge pump, and a long hose to reach our kitchen sink. The bilge pump gets 12V power off the battery in the UPS that keeps the tank running during power loss. I hacked the UPS to provide fused 12V out and ran a power switch up to the the valve manifold.

Hacked UPS, notice the speaker wire for 12V out.

The process to change water is as follows:

  1. Shut off the filter pump and close off the valve leading to it.
  2. Open up the bucket fill valve to let tank water drain into the bucket by gravity.
  3. Once the bucket is full, close the tank valve and open the bilge pump and hose valve. Extend the extension hose to the kitchen sink and turn on the pump to drain the bucket.
  4. When the bucket is empty again, attach the extension hose to the faucet, open the bucket fill valve and close the bilge pump valve. Turn on and fill the bucket with fresh water.
  5. Once full, close the hose valve and open the bilge pump valve. Turn the pump on, which now just circulates water in and out of the bucket. Add water treatment and salt to the water, with the pump providing the mixing.
  6. Close the bucket fill valve, open the tank valve. Now the running pump moves the new saltwater up into the tank.

The whole operation takes minutes and saves us from breaking our back lifting buckets to the bathroom.

Here are some pictures of the system:



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  1. 18 Comments.

    • DermeNo Gravatar says:

      Ha Ha, I Like it! After spending many hours changing water I can see the benefit, but then it would probably take many more hours to set up. 😉
      Keep up the Good Work.

    • BillNo Gravatar says:

      This did take an hour or so to build, but now it’s quick to change water, and we are not breaking our backs carrying buckets to the bathroom and back.

    • LevaNo Gravatar says:

      You use water from the sink, without any filtration? How do you measure your salinity if you barely mix the change water? Just curious as I am getting tired of lugging buckets around.

    • BillNo Gravatar says:

      No filtration. But you could add it if you want to.

      Once the bucket is full of sink water, the bilge pump circulates water in and out of the bucket, mixing it vigorously. That’s when I treat it to remove chemicals, and add salt.

    • Sonny BurnettNo Gravatar says:

      What about a “how to do it” video on youtube, pal?

    • […] is exchanging a portion of the tank’s water on a regular basis. [Bill Porter] came up with a water exchanger that means less manual labor, but makes the process just a bit more […]

    • GregNo Gravatar says:

      You do NOT have to change out 10% of the water in a salt water tank every week. That’s ridiculous! I’ve been keeping reef tanks for years and I do a 10% change a month on my 125 gallon system. This depends on your bio load but I only have 4 small fish (two false percs, one yellow tang and one lawnmower blenny) and some LPS coral and two SPS coral.

      All are thriving but I have a fairly high end direct feed skimmer and I don’t over feed.

      I use RO/DI filtered water from my setup under the sink and it’s easy to siphon 12.5 gallons from the sump and then refill by using a small pump in my container where I pre-mix the salt. Don’t overthink this stuff man… my method is more simple.

    • BillNo Gravatar says:


      I don’t do it EVERY week, more like 2-3 times a month. And I do have more then 4 fish. 10% for me is about 4 gallons, which is a perfect amount to mix in a 5 gallon bucket.

      And I’ll argue my method is just as simple as yours. Pump, container and hose to a sink is something we share. I just taped into my closed canister filtration system with a manifold, You probably dump it in/out of your sump.

    • JoeNo Gravatar says:

      @Greg: What works for you may not work for others or may not be the best conditions for your fish. Simple can keep fish alive, like cats can be kept alive in a cage, that doesn’t mean it is recommended. 4 fish in 125 gallons is why you are an exception. Isn’t your “fish per inch” way under what the average person tries to keep?

      Many people I’ve spoken to with aquariums tell me they get away with rarely if ever changing water, they seem to shun me for wanting to exchange 15% a week as recommended by everyone but themselves (freshwater, not salt). I can’t stand people who treat their pets like that, but many seem to not react if they don’t see a direct threat or impact visible to the naked eye.

      10% for me is 5.5 Gallons, but I’ll often do 2.5-3x that amount for my planted tank. I have a 20 Gallon brute bucket on rollers that I syphon water from the tank into, then after dumping, fill back with treated water and refill the tank using a cheap pond pump and some 3/4″ tubing.

    • MarkNo Gravatar says:

      Have you thought about automating the process?
      I don’t know all the problems that would come up, it might not be practical at all.
      But you could use servo motors controlled by a microprocessor for the valves, and something akin to automated pet food dispensers for the water treatment and salt.

      • BillNo Gravatar says:

        I would have loved to automate it, but it was outside my budget. You have to be careful what electronic valves you use. Also, I was a bit leary of a malfunction that might result in the loss of fish.

    • KeithNo Gravatar says:

      I can understand the concern over the loss of fish. Might I suggest a “Semi-Auto” kind of system? Automated but subject to the push of a button, not the decision of a microprocessor. Additionally, you could use the microcontroller to monitor the levels in the water and trigger an alarm when it senses that a water change is warranted.
      As per usual, awesome work and a great example of ‘creative problem solving’. Keep up the great work.

      • BillNo Gravatar says:

        Hi Keith,

        I had wanted to do it semi-electronic, the biggest obstacle was finding affordable fish safe electronic valves. I discussed possibilities with my local fish store owner and friend and we couldn’t think of a fish safe valve what was inexpensive. He warned again sprinkler valves as they most likely have unsafe parts and have issues requiring a certain amount of back pressure (or lack there of, don’t remember which) to operate.

    • hcl tankNo Gravatar says:

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    • […] new this $20 Amazon special might not be the greatest? With my salt water fish tank feet away, I (poorly) decided it’s $300 LED light bar would be a good load to test my new […]

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