We all do our best to have the proper filtration and life support system to minimize the need for water changes – at least we do ;) But at some point in the life of an aquarium a water change is necessary to refresh the system with new clean water and replenish some elements in the aquarium water. In the article we will cover some of the basics about water changes and share some simple techniques on how to perform a water change.

Why do we change water?

To answer this question we will look at the two typical saltwater aquariums…the ones we call Fish-Only or FOWLR (Fish-Only with Live Rock) and a Living Reef Aquarium. For aquariums that only house fish, the water change is performed to improve water quality…specifically nitrates and phosphates. Occasionally, if a problem exists with PH or another issue with water parameters, a water change could help as well. But for the most part, it’s to improve the quality of the water. Living Reef Aquariums will benefit in the improvement of water quality as well, but in most cases it’s also a way to add calcium and bicarbonate and to replenish some essential elements living corals require.

How much water should we change?

We often encounter new clients who hear “water change” and immediately assume 100% of the water is going to be replaced – that is not the case. We use the phrase loosely but for the most part it refers to a water change of approx 10% – 30% of the aquarium volume. We feel that under normal circumstances 30% should be the maximum so that we do not stress the animals in the aquarium.

Saltwater Sources – How to get it or how to make it?

There a few ways to source or make saltwater. Many folks simply drive down to the aquarium store and buy saltwater by the gallon – that is very practical and inexpensive especially if you have a smaller aquarium. Here in Southern California, there are companies that can deliver saltwater to your home or business. In some places like Hawaii or Florida, water could be collected from the Ocean. One could also mix saltwater at home with an aquarium salt mix from brands like Instant Ocean or Red Sea. We always recommend using RO/DI water to mix the saltwater to have the best quality water possible.

So how do you do a water change?

For most aquarium systems it’s a very simple process. First, turn off all power to the aquarium including all heaters, pumps, etc. Next, using vinyl tubing (we like to use 3/4″ – 1″) clamp one end inside the aquarium and run the other end to a drain location such as a sink or a toilet. Next, suck on the hose as hard as you can for a couple of seconds to get the water to siphon, place the hose in the drain and you are now removing water. The first time this is done you might want to use 5g jugs or some container with gallons marked on it so you could measure the number of gallons – once you have that information you can mark the aquarium with a sharpie so you know that specific marks equals a certain volume of water removed. Now that you have removed the water, simply add the same volume by using jugs or buckets. You could also use a small submersible aquarium pump and vinyl tubing to pump water back into the tank. When that’s completed , turn on all the power to the aquarium and you’re done :)


Water changes are an important tool for any aquarist. We want to perform this task in a practical manner so that it’s easy and could be done with minimum effort. We hope some of the information we’ve shared here would help you with your water changes :)