Water Changes

One of the best ways to reduce pollution in our saltwater aquariums is through regular partial water changes.  Dilution is indeed the solution to pollution, but ask any experienced aquarium keeper and they will tell you that changing water is one of the things they least enjoy about the hobby.

The key benefits to regular water changes are:

  • Nutrient limitation
  • Dilution of various pollutants
  • Replenishment of trace elements

Water Changes And Nutrient Limitation

As mentioned on our page on Algae Control, the waste products of fish, overfeeding, a poorly functioning biological filter and a lack of regular water changes all contribute to a buildup of nitrogenous compounds in the water.   These compounds, in the form of nitrates and organic phosphates become nutrients for nuisance algae.

water changes

Water changes keep this 30-gallon aquarium healthy


Regular water changes are necessary to reduce nutrients that cause algae to overrun our aquariums!

Water Changes To Reduce Chemical Pollutants

There might come a time when we have to deal with chemical pollutants that accidentally enter our aquarium.  Insect sprays, pesticides and even bleach and window cleaner solution are some of the common household chemicals that have been known to find their way into aquariums when used carelessly.

In the event of chemicals entering our aquarium, a large quantity of activated carbon, Poly-Filter and several massive water changes might help alleviate loss of livestock.

Water Changes To Replenish Trace Elements

Trace elements in aquarium water are constantly being metabolized by corals and algae.

While we could replenish trace elements using any number of commercially available additives, the risk of overdosing is always a possibility.  Overdosing of trace element additives is always followed by an algae bloom.  On top of that, there is no telling how long that bottle has been sitting on the shelf, unrefrigerated.

Using a good synthetic salt mix ensures that we are replenishing important trace elements with each water change.  And you can always tell a fresh batch of salt mix by its fine texture and lack of any clumps that might indicate that moisture has entered the container.

Water Changes — How Much To Change

Actually, the jury is out as to how much water to change.

Some hobbyists seem to run their tanks successfully for years without any water changes.   But there are several things that these tanks usually have in common —  lots of live rock, vigorous protein skimming and a small fish population relative to the size of the tank.  These no-water-change tanks are also usually quite mature, at more than 3 years old.

For the rest of us who like a reasonably well-stocked tank — and also because we like to feed our fish — 10% weekly water changes in the first year of our aquarium’s life is very beneficial.

After the first year, provided we haven’t overstocked our tank with fish, water changes of 10% to 15% every month should suffice.    Again, lots of live rock, efficient protein skimming and a healthy biofilter will help alleviate any problems should we lapse on our monthly water change regimen.

Don’t Change Too Much Water At One Go!

Remember, it’s all about partial water changes of 5%, 10%, or at most, 15% at a time.   Changing too much water all at once will stress your corals and invertebrates.  Although fish seem to take to large water changes better than invertebrates, provided that pH and salinity of the new water are properly matched.

Regular partial water changes are the best way I know to keeping a saltwater aquarium and its inhabitants in the best of health.

Read more about Saltwater Aquarium Maintenance:

Algae Control

Feeding Marine Fish

Mixing Saltwater

What To Look For In An Aquarium Salt

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