Saltwater Aquarium Water Change: a Maintenance Cornerstone

Buckets and a siphon hose - simple, low-tech water changes

Buckets and a siphon hose – simple, low-tech water changes

When it comes to maintaining exceptional water quality and healthy, vibrant livestock, marine aquarium hobbyists have no greater ally than the humble water change. No filter, skimmer, reactor, ozonizer, UV sterilizer, or any other “izer” should be considered a substitute for the simple process of siphoning out and replacing a percentage of your aquarium’s water on a routine basis.

Regular water changes provide a myriad of benefits. Among them:
  • Diluting nitrate, phosphate, and other dissolved pollutants
  • Minimizing troublesome algae outbreaks by exporting the aforementioned dissolved pollutants, which serve as fertilizer
  • Replenishing all the minerals and trace elements vital to the health of marine livestock
  • Replenishing pH-buffering compounds
  • Improving water clarity
  • Helping to keep fish and invertebrates as healthy and happy as can be

The list goes on and on! In essence, water changes take out the bad stuff and replenish the good stuff, and there’s really no downside to them. There’s no water-quality issue or livestock ailment that isn’t made at least somewhat better by a water change.

How much and how often?

The appropriate volume and frequency of water changes for any saltwater system depends on several factors, such as the stocking level, feeding frequency, sensitivity of the livestock, etc. But a good rule of thumb is to change at least 20 percent of your aquarium’s water volume every two weeks (or 10 percent every week). If that doesn’t suffice to keep nitrate and other dissolved pollutants at the desired levels, you can always do larger or more frequent changes. Let your test kits be your guide!

How do I remove the water?

A good-old-fashioned aquarium siphon hose with a vacuum attachment at the end is ideal for performing water changes. Simply siphon out the desired amount into a bucket and dump the dirty water down a floor drain or sink. If the idea of hauling buckets of dirty aquarium water doesn’t appeal to you (or your back), you can also use one of the various water-change systems on the market. These products come equipped with a long hose that connects directly to your faucet and utilize the faucet’s water pressure to create the siphon.

While vacuuming, try to capture and remove as much detritus as possible from the substrate. If you have a fine-grained substrate, take care to keep the vacuum attachment above the surface. Otherwise you’ll suck substrate material right out of the tank. It’s also a good idea to scrape or brush off any algae that’s growing on the tank sides and/or rockwork just prior to a water change. Then you can easily vacuum out the loosened bits and clumps along with any other debris.

Once you’ve siphoned out the desired amount of dirty water, go ahead and refill the tank with an equal volume of clean salt water. Your replacement water should be mixed up at least a day ahead of time (ideally using RO- or RO/DI-purified tap water), heated to the same temperature as your display tank, and aerated.

Simple but so important!

That’s all there is too it! Pretty straightforward, huh? Simply staying on top of those routine water changes will go a long way toward ensuring your success in the hobby.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Gus Gutierrez says

    Aphasia-X is an effective aphasia eliminator if on a small scale infestation or effective reducer to tolerable levels but it’s delivery syringe system leaves a lot to be desired. It is hard to manipulate that little syringe in the middle of the aquarium. Solution: use a plastic tube coral feeder with a rubber ball squeezer on top. It’s about 18 inches long. Suck your chemical and bomb away. Very effective delivery system,

  2. Should you do weekly water changes to a new tank while its doing its first cycle?

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