How to Change Fish Tank Water Without Killing Fish, Be a Pro

How to Change Fish Tank Water Without Killing Fish

The morning turns into mourning when you see one of your beloveds floating upside down. Oh, the poor fish is dead! Everything was right since you fed them one final time, said goodbye, and went to sleep. You wonder what went wrong!

Suddenly you realized you performed a rigorous water change last day. Was something terrible associated with this action? Did the water change kill your fish? Apparently, yes, but the actual answer is more explanatory than that.

Have you heard a tale of woe about the aquarium keeper who lost all his fish after a water change? He was doing fine without a partial water change even since he set up the tank over a year ago.

One of his friends noticed the substrate looks dirty, and the aquarium owner came to know he should have been doing regular water changes. The owner immediately took action, changed all the water, and cleaned the aquarium thoroughly.

Everything looked immaculate, and the owner was thrilled. But the next morning, half of the fish died, and the rest died within a week! The owner anguished to see all the dead fish and his advisor friend blamed the tap water for being lethal. Was it really so? Let’s dig a little deeper.

Why did water change kill fish?

The sudden alteration in water chemistry and aquarium temperature is the culprit for fish’s immediate death after water changes. Also, water changes can destroy the established healthy cycle in aquariums resulting in added toxicity and stress. The further fatality comes from the second reason.   

Sudden change in the water chemistry

An unanticipated drastic change in the water variables imposes tremendous stress on fish. It is more damaging if you haven’t changed the aquarium water for a very long time and then replaced everything straight away.

An aquarium is a micro-ecosystem in which several biological and chemical processes are taking place continuously. Fish wastes, food leftovers, and dead plant matters alter the water parameters over time. If this change is slow, fish can somehow be accustomed to it.

Though you are adding the purest water to the aquarium, the pH, hardness, and other water parameters shift from the previous condition. Fish might not tolerate this change and die. Poor pets were attuned with some pollution, so the freshness is killing them!

Temperature shock

Another potential reason for fish getting killed by water changes is a sudden down in water temperature. When adding new water to the tank, it is vital to maintain the same temperature as the previous condition. 

If the degree of temperature difference is vast, some fish may die going into shock, while others may succumb to disease over the next few days.

Losing beneficial bacteria

Inappropriate water changes are the slow killer of fish in another way. Over-frequent water change can kill off beneficial bacteria in the fish tank. Beneficial bacteria are essential to establish a nitrogen cycle that prevents toxicity from evolving in a fish tank.

If you remove all the water and thoroughly clean the aquarium, it could kill off the majority portion of beneficial bacteria. A fish tank that is deficient in beneficial bacteria requires recycling. Otherwise, toxicity builds up rapidly, and the water quality deteriorates. The entire process becomes harsh on fish and weakens them.

Pathogens presenting in the fish tank might not miss this opportunity to kill your fish. If your routine water changes are too frequent to allow growing beneficial bacteria, the result is the same.

Why should you change the water then?

If changing water can potentially be fatal for fish, should you do it at all? The answer is, yes, you should do regular water changes for the long term health betterment of fish. Dissolved toxicity in the aquarium water not visible in naked eyes, cannot be eliminated unless adding some freshwater. 

Dissolved toxicities are slow poisons, not killing your fish then and there, but they reduce fish’s immunity and, eventually, the lifetime. Okay, let’s discuss a bit more in-depth.

Fish secrete waste, and it goes nowhere but accumulated at the bottom. While you are feeding fish, if they can’t take all the food within a few minutes, food leftovers join with fish wastes at the tank bottom. 

In all feeding instructions, it is clearly briefed to feed fish as much as they can finish in five minutes, which is a very vital instruction as prepared fish foods like flakes or pellets don’t float for hours. If your fish don’t consume floating foods right away, it will sink at the bottom to be wasted.

All the aquarium wastes start breaking down at a point and decompose to ammonia. Ammonia is a highly toxic gas that persists in the water dissolved unless beneficial bacteria convert it to nitrates. The entire biochemical process is known as the nitrogen cycle. Establishing a nitrogen cycle is essential to an aquarium for healthiness. 

The toxicity of ammonia is acute and fatal. Nitrates are less deadlier than ammonia, not killing the fish outright, still harmful, and has to be eliminated.

Live aquarium plants can consume nitrates naturally. Always, it may not be sufficient. The only effective way to remove nitrate from the tank is to do so literally through water changes.

Another crucial reason you should do regular water changes is that it can oxygenate the aquarium water. An oxygen-rich aquarium is a healthy environment for fish. Fish require oxygen just like you and us. They can’t breathe, but they have a distinct process of taking dissolved Oxygen (DO) from the tank water.

 The aquarium water condition impacts a fish’s immunity system directly. A healthy fish with strong immunity will rarely get sick.

How to change fish tank water without killing fish

Acclimatization is the key! Don’t inflict your fish on a sudden change. Despite a small risk that it might harm your fish, regular water changes are incredibly crucial. 

You cannot compromise subjecting your fish to poor water quality, and you cannot risk their life. So, you have to know how to perform water changes in a balanced way. Be mindful of four basic things. 

How to Change Fish Tank Water Without Killing Fish

Step-1: Do only partial water changes

Small water changes regularly are pretty effective than a massive water change once in a while. I suggest changing only 10-15% of the water every week. To eliminate any excess nitrate buildup, it is safe to perform one-third of water change monthly.

I’ve found it’s a perfect routine with no sudden change in water condition and not losing friendly bacteria. Partial water change this way is great prevention of nitrate buildup without disturbing your fish.

Step-2: Use a gravel vacuum

People make a mistake changing all the water when they go through a thorough tank cleaning, including the substrate. They find no better alternative to clean the substrate without removing tank water. 

It is advisable to use a gravel vacuum to suck out debris from the bottom once a month while performing the major cleaning.

A gravel vacuum is a useful tool to perform water changes and substrate cleaning, so invest in a better quality tool. Siphoning does water changes along with cleaning a fish tank conveniently.

Step-3: Care about the water chemistry

Water chemistry is crucial for the fish’s health, and a drastic change can be deadly. Therefore, maintaining a steady condition before and after the water change should be the top priority. 

Before you add new water to the aquarium, perform a simple water test to analyze pH with a testing kit. Though several parameters control the water quality, pH is the key indicator. 

If you add tap water, don’t forget to treat the replacement water with conditioner. Effective water conditioners are readily available in the market. The aquarium water needs to be free from chlorine and heavy metals.

Step-4: Maintain a steady temperature

Always try to keep the new water temperature as close as possible to the current aquarium water temperature as a quick change in temperature can be severely stressful for fish. 

For most tropical fish, the acceptable temperature ranges from 72° to 80° Fahrenheit. Fish are more susceptible to diseases at low temperatures.

You can easily measure the water temperature with a thermometer. It is better to preheat water before adding it if necessary. 

Water change sequential steps

Fish tank water change steps

Arrange tools

The primary tools for water changing tasks are siphon and a bucket. Siphon type gravel vacuum is handy for this chore. Additionally, a water conditioner and a preheater to prepare refill water are necessary.

Prepare new water

The preparation of new water to refill the aquarium is the crucial step. Tap water is perfectly okay if it is chlorine-free. Because chlorine compounds are deadly for fish.

It is better to use a water conditioner or de-chlorinator. When using a water conditioner, don’t forget to choose a reliable brand, and follow the manufacturer’s instructions to the letter.

Once the water is ready, give a final inspection. Check the pH and water temperature. If the water is too cold, preheat before adding.

Siphon out water

Place the suction of the siphon just above the substrate layer and suck water from the bottom. I recommend a 30 – 40% water change every four weeks. Keep in mind that changing more than 50% of water at a time is not wise.

Add water to the tank

The final step is pretty simple. You have prepared bucketful water to add it to the aquarium. Found the pH, and water temperature is just perfect as you desire. Now add it to the aquarium, and your job is done.

Take away

Now you perceive that water change is not any dangerous business, but rather an absolutely essential part of fishkeeping. You have to perform it in a way so that fish can adapt to the change. 

A sudden change in water chemistry is the primary cause of fish deaths after water changes. But fish deaths after a water change is avoidable.

The key that gives the best result for a water change eliminating associated risks is a routine. When you follow a meticulous routine for water changes, your fish will be easily habituated with it. Good quality of water can keep your fish healthy and lively with a longer lifespan.

No more heartbreaking scenes of dead fish floating in the aquarium! Do regular water changes and do it correctly. Water quality in an aquarium is uncompromisable. Happy fishkeeping!

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Sujit Modak Aquarium Tales Owner
Sujit Modak

Hello, everyone! Welcome to my aquarium blog. Fishkeeping is my passion, and I started this fascinating hobby back in 2006. Besides my engineering profession, I deeply studied many fishkeeping topics since I started building my home aquarium. I researched effective aquarium filtration and lighting of planted aquariums. I am keeping 20+ species of freshwater and saltwater fish as my aquatic pet collection. I successfully experimented with a complex ecosystem inside the aquarium, biotope aquariums, aquaponics, etc. I would love to share some learnings from my hands-on experience of the last 14 years. Hopefully, my sharing will be somewhat helpful to make your aquarium journey awesome! 

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