They are what is known as Ectotherms which means that their bodily functions are entirely dependent on outside temperatures. It’s why most disease outbreaks in aquarium fish happen in Spring and Fall when the temperature difference between day and night is greater.įish are cold-blooded creatures and do not regulate their body temperature. Water temperature fluctuations are the major reason for most of the fish who fall ill, seemingly out of nowhere. To find out whether the drastic change in Nitrate stressed your fish you could use a liquid water test kit before and after replacing the aquarium water. This weird behavior may even be accompanied by spasms. Impaired osmoregulation may also explain why your fish are swimming erratically and acting stressed after a water change.

In fact, impaired osmoregulation is often the reason behind a bloated Betta fish. The swollen organs could put pressure on the swim bladder of the fish which may lead to it swimming upside-down or sideways. When in Osmotic shock following a water change, freshwater fish will hold too much fluid, which may lead to swelling of their organs, a condition known as Dropsy. Osmotic shock may be the reason why fish suffer when you remove a large portion of the Nitrate ions through changing the water in their tank. Osmotic shock is the condition where the body of a fish fails to regulate its absorption of ionic compounds and starts to either absorb or release too much fluid as a consequence. A saltwater fish regulates its body in a way that prevents it from absorbing too many salts from the water since the water contains more ions than its body (salts are ionic compounds). Osmotic Pressure works both ways and changes directions when it comes to saltwater fish. Here’s an illustration of how Osmoregulation works in freshwater fish: The fish’s ability to counter osmotic pressure is called Osmoregulation. However, under normal conditions fish have a mechanism that protects them against this phenomenon. It’s why you never want to use distilled or purified water for water changes in your aquarium. This means that without bodily fluid regulations the surrounding water will try to get inside of the fish’s body while sucking the ions from it through a phenomenon called Osmotic Pressure. The body of a freshwater fish contains more ions and ionic compounds than the water surrounding it. Nitrates are ions (NO 3-) and fish can gradually adapt to changes in the level of ions and ionic compounds such as salts in their environment. However, the sudden drop of Nitrate levels that follows a water change could send your fish into Osmotic Shock. Nitrate levels were too high before you changed the water.Ī high level of Nitrate in the aquarium water can be inherently toxic to fish and may even kill them. Here’s which water parameters may be responsible for your dying fish: 1. There are multiple things that could go wrong during a water change. What water parameters changed so suddenly as to kill or stress your fish? Any strange changes in their behavior can be the signs of a dying fish. This could happen even with a smaller water change, as long as a considerable amount of time has passed since the last one.Īuthor’s note: Even if your pet fish don’t die immediately after you change their water, it’s a good idea to monitor their behavior for signs of stress.

The fish may not be able to adjust to the sudden shift in these parameters and may get severely stressed or even die as a consequence. However, changing a large portion of aquarium water may significantly alter the parameters of the remaining water inside the tank.

If your aquarium fish die after a water change it likely has to do with the sudden shift in water parameters:įish can adjust to gradual changes in their environment. The main purpose of changing water is to remove Nitrate from the tank and also regulate the everfalling pH that results from the activities of different bacteria. Water changes are beneficial to the aquatic inhabitants of the tank but only when they’re executed properly. This however doesn’t mean you shouldn’t strive to maintain healthy water quality in the tank. Performing large or infrequent water changes in an aquarium may indeed kill the fish inside. Why did your fish die or suffer after a water change? Truth is, there’s more than one thing that could go wrong when doing so. So why are your fish dying right after you’ve changed the aquarium’s water? Cleaning your aquarium and maintaining it in good shape is essential for its long-term success.īut then why do fish suddenly die or get very stressed after a water change?Ĭhanging the water in the tank should be a good thing and not lead to shock or fish deaths.

Goldfish tank water change