How to Save Dying Fish after Water Change


If change is difficult for David Bowie, then a water change can definitely be difficult for your fish. While fish in the wild can sometimes adapt to changes in their environment, aquarium fish are far less likely to do this and, as we’ll see, when they do they require a lot of time to get through even mild changes.

If you’ve ever suffered through the sad case of fish dying as the result of a water change, you know this all too well.

So, how do you save dying fish after a water change? And how can a water change be made safe so they don’t kill your fish? If your fish is fast dying after a water change, what if anything can be done to save it?

How to Save Dying Fish after Water Change, Aquarium Fish Tanks UK

What Happens During an Aquarium Water Change?

Changing the water in your aquarium is usually as easy as swapping out a percentage of the aquarium water and replacing it with fresh tap – treated water. Changing aquarium water is often used to remove waste and dirt, dilute the build-up of toxic elements and increase oxygen levels in the water – often great for aquarium life.

In some cases, changing the water in your aquarium can result in your lovely aquatic pets dying from the sudden change in pH levels in their home.

It’s a situation that is best avoided.

Of course, the most obvious way to deal with this problem is to never have it arise in the first place, and on the surface that seems like it should be the easiest course as well. As it makes no sense whatsoever to have a water change in an aquarium kill fish?

Most pet fish owners know that fish don’t like to be kept in disgusting, scummy conditions (who would?). So what does this mean?  It means that cleaning your fish tank and changing the water is something that needs to be done on a fairly regular basis. However, far too many first-time fish tank owners change the water in their aquariums, only for this to lead to a full-blown fish-apocalypse over the coming days as several or all of their fish die.

Why do Fish die after a Water Change?

In short, it happens because while your fish can deal with changes, they can’t deal with rapid ones. Imagine being taken out of your cosy home and suddenly being thrust into Arctic conditions of double-digit negative temperatures.

That’s a rough estimation of what your fish are going through when you suddenly perform a wholesale tank change on them. This is especially true of saltwater tanks, where the balance between the salt levels, water levels, and any plant and algae life in the tank needs to be kept at such a precise level.

But wait – humans survive in Arctic conditions, and fish can survive tank changes, so why don’t they in this case? The key here is the time that change takes to occur. When humans go into the Arctic, we don’t just go from 75 degrees Fahrenheit to -20 with no clothes to protect us. Arctic explorers manage temperature changes slowly and wear thick protective materials while doing so.

Likewise, your fish can survive a water change, as long as it isn’t done too quickly or all at once.

How to Change Your Water Safely

All water changes should be done as slowly as possible. At a maximum, you should only be changing about 5% of your fish tank’s total water content, to begin with. Following that, only 10% to 20% is required if the initial water change occurred without incident. Then it will be wise to wait an additional week before changing more water in your fish tank.

To put this into context, it also means you will need to change the water more frequently than just “once in a long while”. Which, to be fair, most fish tank owners do anyway.

Despite the key points above, there’s another sticking point to bear in mind when it comes to you changing your fish tank water and your fish dying as a result. As aquarium plants are added or decay, fish waste and algae accumulate, and other factors take place, the tank’s pH composition gradually alters, and your fish slowly adapt along with it.

As such, even if you change the water slowly, you doing so without accounting for the new consistency to which your fish are accustomed can be a huge problem. It is important to keep an eye on your fish tank measurements of the water, PH, salt, and other vital readings prior to changing out the water in your tank. A good aquarium test kit is an important tool to have with you to do these checks.

Tips to Save Dying Fish

Bearing the factors listed above will help you avoid the possibility of damage in the future, but what do you do if your beloved pet fish is already?

Some treatment options available include:

  • Place it in a bowl or tank with a water level similar to the water you just changed
  • Do everything possible to decrease its stress level
  • If possible try putting your fish in an aquarium with a similar pH level and climate to its previous home
  • Keep your dying fish in isolation, to avoid the chances of spreading the problem to other fish or stress the dying fish

As shown above, you can save dying fish following a water change in your aquarium. The key thing is that when those changes occur too quickly, it can have lethal consequences.

Small, timely water changes on a week to week basis are your best bet to help avoid having dead fish following a water change.