The Age of Your Aquarium Matters - Old Fish Tank Syndrome

man feeding fish in aquarium

Here are a few questions for you, which will tell you exactly why you landed on the right page before experiencing the most mind-boggling fish keeping disasters. Has your fish tank been running for long? Whenever you add new fish to the tank, do they die within a few days? Have you been a bit busy and did not have the time to run tests on the tank's water parameters?

If the answer to all of the above questions is a single, big YES, please stay put. We are unraveling another mysterious ailment that might have made you doubt your fish keeping practices, the twentieth time today!

Typically, all sirens of caution on the web worn beginner fish hobbyists of the many newbie mistakes that can hinder their experience. However, today we are taking up a case of an established fish tank. As your aquarium setup ages, it becomes prone to an unexpected condition called the old fish tank syndrome.

In this article, we talk about what is old fish tank syndrome, what causes it, how you can prevent or cure it as well as some bonus tips that will ensure you have an ideal fish-keeping experience. Follow along!

What is Old Fish Tank Syndrome?

Old Fish Tank Syndrome is used to explain the insufficiencies that occur in closed aquarium systems over time. The condition is strongly marked by constant ammonia and nitrite spikes and low pH levels within the fish tank.

In brevity, the syndrome occurs when the integrity of healthy water parameters is compromised due to a lack of fish tank maintenance. An aquarium that has been functioning over time is naturally expected to be well established and balanced. However, on the inside, the water parameters are slowly taking a turn for the worse.

What Causes Old Fish Tank Syndrome?

The concept of old fish tank syndrome is quite simple to grasp. Your aquarium is a closed ecosystem, quite similar to your home. Richy, a marine biologist and founder of AquariumStuffs, explains old fish tank syndrome in the simplest way possible - "When you first moved into the house, everything was in the best state possible, healthy, clean, and well-balanced. However, as you begin living in the same place, things start to accumulate with time, leading to a messy situation. Well, especially when you are busy or a bit inconsistent with the cleaning routine. Now, position the same scenario in the tank; all the build-up, including toxic elements and waste, remain within the tank until you take proactive steps to maintain healthy water parameters by taking out all the accumulated toxicity from the aquarium."

Yes, your filtration system is responsible for doing the clean-up job in the fish tank's water. Perhaps you have employed the best types of filtration methods and several other systems to ensure the water is constantly cycled. Even the good bacteria are working their best to convert the harmful gases and elements into less toxic components. But the waste is still present in your filter media unless you rinse it in clean water. Although in their less toxic state, the products converted by the good bacteria are still present in the tank unless you conduct partial water changes regularly.

The key takeaway is that – what goes and builds in your fish tank stays there until you take it out. If you are not much of a reader, here is a quick overview of all the evils that cause old fish tank syndrome:

  • Poor fish tank maintenance
  • Irregularity in conducting water changes
  • Clogged aquarium filters
  • Overfeeding
  • Low pH levels
  • Lack of water testing

Old fish tank syndrome creeps in at an awfully slow pace, allowing the tank inhabitants to get used to the environment over time. The slow onset of the condition is one of the primary reasons why it remains unspotted by fish keepers for a long time.

What are the Symptoms of Old Fish Tank Syndrome?

When your aquarium succumbs to old fish tank syndrome, some of the more apparent symptoms can include the death of fish recently added to the tank. In contrast, the older tank mates remain relatively unaffected. The older inhabitants are accustomed to the teetering water chemistry and have built mechanisms that combat stress or relevant aquatic illnesses. However, the newly added fish are not habituated to unhealthy water parameters and go into shock, which causes stress, often leading to death.

Here is a list of the technical symptoms that indicate that your aquarium is under attack by all the vices of old fish tank syndrome:

  • A significant spike in nitrate and phosphate levels
  • Low or acidic pH from that of the healthy regular units
  • Low carbonate levels
  • Presence of ammonia and nitrites in the tank
  • Absence of the essential trace elements necessary for a healthy aquarium set up
  • Absence of all biological filtration activities

Unaware of the condition, fish keepers may feel that the aquarium is healthy as the tanks' older residents are well and alive. However, as you begin to add new inhabitants to the tank, they are guaranteed to succumb within a short period.

You would assume that the new fish might be unhealthy from the get-go and remain oblivious of the disaster within. Most fish keepers, who decide to act, might conduct a complete fish tank water change or cleaning, hoping that would reset the conditions back to normal if anything at all is amiss. Guess what happens next! The old fish begin to show signs of stress too. Why? Because now they are experiencing a complete change of environment and go into shock!

Before you make the same mistakes, that will cost you even more finny lives. Here is a list of the best remedies for old fish tank syndrome.

How Can You Prevent Old Fish Tank Syndrome?

Generally, fish keepers put their ultimate faith in the agreed-upon percentage and frequency for conducting water changes. However, it is essential to understand that your aquarium setup is unique, and so are its needs. Following the same sentiment, a low stocked fish tank with a few aquarium plants will have fewer requirements for water changes than a heavily stocked fish tank.

This brings us to the next significant dilemma- How do you know what is right for your fish tank? Water testing for the correct parameters is the best way of remaining aware of what's going on in the aquarium. If you are on the right mark with the water changes, the nitrates will always remain below 5 to 10 ppm (20mg per liter). However, if the levels spike even the slightest, it is a strong indicator that you need to conduct more frequent water changes.

Constant Water Testing + Regular Water Changes = The best formula for preventing old fish tank syndrome!

How Can You Treat Old Fish Tank Syndrome?

"Rome wasn't Built in a Day" is a saying that teaches your patience and perseverance! Why are we bringing this up here? Well, that saying should be your mantra when you are on the mission to rectify old fish tank syndrome!

Here is the catch - We have already seen that in the case of old fish tank syndrome, all the new fish you add to the fish tank die in a few days because they are not used to the unhealthy water parameters and go into shock. However, the old fish remain well and alive because they were accustomed to the environment, albeit a bad one in the aquarium. Meaning, when you are curing the condition, conducting complete water changes, or suddenly changing the fish tank environment, it will cause stress and shock to the older residents in the tank.

The tank will be remitted, yes, but all your fish will most probably die. So, what do you do?

Take it slow - that's the best approach. Start by conducting 10 or 15 percent water changes every day. If you catch an ammonia spike during the process, halt the water changes for a few days.

Slowly but surely, the water parameters will begin to improve, and that is your sign to take the filter media for a partial cleaning process. Don't be thorough, and we stress that. You still want to keep the good bacteria in the filter intact. If you remove all of the healthy aquarium bacteria from the media, your aquarium will go into another mini-cycle.

While you are still in the process of correcting old fish tank syndrome, feed your finny friends lightly. This will ensure no decay of the uneaten food, which will otherwise lead to further ammonia and nitrite spikes.

As things begin to improve, stick to a regular but firm fish tank maintenance and water testing routine.


Time, routine, and maintenance are critical covenants for an ideal fish keeping experience. Old fish tank syndrome is a product of relaxed water changes and fish tank care on the part of the fish keeper. The condition is easy to treat if you follow a slow but strict schedule on water changes. You never know, the most basic tasks and routine might be the very things that will save you from experiencing the death of a finny friend.