What is Old Tank Syndrome?

Aquariums are an excellent addition to any home, but a lack of maintenance and care could turn it into a nightmare. Old tank syndrome develops when an aquarium’s environment and water quality degrade over time, causing water acidity to rise and weaker fish to die out.

This phenomenon isn’t something that you’ll notice in your aquarium right away. Your fish will probably look normal swimming around in their semi-murky water. However, a quick water test will tell you a different story – one that should alarm you.

The term “old tank syndrome” refers to successive water quality changes in an aquarium – due to high nitrate levels and an accumulation of scum. Closed aquariums that haven’t been appropriately maintained render their filtration systems useless. This makes nitrate levels rise, the water chemistry drastically changes, and eventually compromises your fish state.

What causes old tank syndrome? 

Every day, fish excrement, excess fish food, and minerals from the water supply build up in the aquarium. Filters help regulate these substances, but if left alone, they will remain stuck in the filter. Unless removed manually, this accumulated gunk will stick around forever.

In addition to this, your primary water source introduces excess minerals and chemicals into the aquarium. While this doesn’t necessarily harm your fish, it can slowly alter the water’s chemistry – raising nitrate and ammonia levels and lowering pH levels.

All of these put together contribute to the degradation of the tank. Simple cleaning methods will no longer do, as the neglect completely transformed the aquarium. Over time, this toxic buildup will eventually turn your peaceful aquarium into a deathtrap.


What changes occur in old tank syndrome? 

One of the most significant contributing factors to old tank syndrome is nitrate. Tanks left with unchanged water will eventually increase in nitrate levels. While nitrate is the least toxic end product of the nitrogen cycle, it can become toxic in higher concentrations.

High levels of nitrate put chronic stress on fish, making them weak and more prone to diseases. As nitrate levels rise, pH levels will fall – acidifying the water. Not only is this harmful to fish, but it could potentially be lethal as well. This change in pH also invites more bacteria to fester in the tank – becoming a potential health hazard to tank owners.

Testing the water in an aquarium with old tank syndrome will show high nitrate, ammonia, and carbonate levels. This imbalance will then result in losing a lot of essential bacteria. The pH level will then show below 6, indicating acidity.


What are the signs and symptoms of old tank syndrome? 

As it turns out, old tank syndrome occurs more often than you think. The reason for this is that it sneaks up on you – beginning gradually until it affects your whole aquarium. The signs aren’t obvious, which is why many owners discover the damage too late.

While you think it may be obvious to spot a dirty tank, there’s more to it than just murky waters. Aquarium maintenance can be such a chore that most owners skip it entirely – relying on filters and only cleaning out the apparent scum. Unfortunately, the real danger is invisible to the human eye.

The most apparent symptom of old tank syndrome is the dying out of newly-added fish. Older fish seem healthy and will survive in the toxic water, mainly because their bodies have become accustomed to the water’s extreme pH levels. They could even have developed a resistance against certain bacteria and chemicals.

However, this water will prove to be too much for new fish. Because they haven’t adapted to the water chemistry in the same way the older fish have, the new fish go into shock when they’re put in the water. This leads to complications and eventually their untimely death.


What happens to fish inside an aquarium with old tank syndrome? 

Since the nasty transformation happens gradually over a long period of neglect, some of the fish in the tank will have enough time to adapt to the toxicity levels. As pH levels drop and nitrates increase, weaker fish die out, and the surviving, tougher fish adapt to the scummy water.

Because the stronger fish manage to adapt, most owners won’t even suspect contamination going on. The most common mistake is that they replace the dead fish with a new batch of fish, which instantly dies because of the water’s toxicity.

While some of the more robust fish will manage to live out the weaker ones, they won’t be in the best shape. Extended exposure to toxic water will cause organ complications. Eventually, these fish will die out as well – leaving you with the task of cleaning up this biohazardous mess, potentially exposing you to bacteria as well. 

small fish


How do I clean an aquarium with old tank syndrome? 

Luckily, there is a way to reverse the effects of old tank syndrome. However, it will take some time. A slow and steady change is necessary for a problematic tank to become better again – because sudden changes will arise to more complications.

Ideally, the water should be changed daily in small increments – around 10%-15%, to allow the fish to adapt. Along with these changes, you should test the water daily for easy monitoring. Test for nitrate and see if they’re dropping. If you notice ammonia levels increasing, it’s best to leave the tank alone so it can re-stabilize.

Once these levels start to look normal, you can start changing the filers. Keep monitoring the water chemistry as you do so. Gradually, you’ll be able to clean out the tank entirely without messing with the equilibrium of your fish. Remember, the goal here is to regulate pH levels, minimize nitrates, and leave no trace of ammonia.


How do I save my fish from an aquarium with old tank syndrome? 

When you clean your tank from all the harmful buildup, be warned that when you put the fish back in, they will all be dead. Abrupt and drastic changes in water chemistry, even if they’re meant for the better, will have devastating effects on your fish.

Fish food and excrement are a contributing factor in the tank’s acidity. During the same time that you’re slowly changing the quality of the water, you should feed your fish in small rations. This way, their biological waste won’t affect the water’s ammonia levels – keeping acidity levels at bay.

In about a month into this procedure, you’ll notice a lot of positive changes. Your tank will smell a lot better, and the water will clear. Pretty soon, you can begin to feed your fish naturally and continue regular maintenance.


How can I prevent old tank syndrome? 

As it turns out, you can avoid old tank syndrome altogether if you pull out all the stops. This is a much better approach than to deal with the toxicity and risks later on. Maintenance, monitoring, and mindfulness are essential.

Ideally, water changes should be performed weekly – around 10% to 15%, unless you’re dealing with a crowded tank. You should remove food particles, fish excrement, and other debris immediately after feeding time. As for tank cleaning and filter maintenance, these should be done monthly.

Along with these, it’s also recommended that you test the water regularly. By monitoring pH levels and the presence of ammonia, you can avoid disaster before it even happens. It’s best to record these findings in a logbook so that you can compare and predict any worrisome patterns.


Will aquatic plants help with old tank syndrome? 

Not only do aquatic plants make your aquarium prettier, but they also balance out the water chemistry in the tank. Adding a few live plants in with your fish will benefit the overall quality of the water. They also drastically improve the well-being and health of your fish.

Live aquatic plants will consume carbon dioxide and produce oxygen, which is vital for your fish. Not only that, they keep pH levels stable, prevent excess algae growth, and remove nitrates from the water. In the long run, you’ll be left with a healthier and cleaner aquarium.

The presence of aquatic plants improves the ecosystem in the tank, especially the health of the fish. Live plants serve as additional nutrients and extra spaces for fish to rest in, boosting their immune systems and relieving them from stress.

Please take note that for aquarium plants to thrive, you will need to care for them as well. They will need moderately soft water, ample exposure to light, and their plant food to grow to their fullest potential. Over time, your tank will develop into a healthy little ecosystem.

Clean an old tank with some new tricks

You can avoid having to deal with old tank syndrome with the proper mindset. By dedicating time and attention to your aquarium, you spare yourself the misery of losing precious fish. Prevention is better than cure, and a little maintenance every day goes a long way. 

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  1.   https://aquariumgenius.com/what-is-old-tank-syndrome-symptoms-causes-and-cure/
  2.   https://www.thesprucepets.com/old-tank-syndrome-1381225
  3.   https://www.practicalfishkeeping.co.uk/features/how-to-avoid-old-tank-syndrome/
  4.   https://www.liveaquaria.com/article/214/?aid=214
  5.   http://www.fishtanksandponds.co.uk/the-basics/old-tank-syndrome.html
  6.   https://www.aqueon.com/information/care-sheets/aquatic-plant-basics
Rita Wagenerhttps://thepetkeepers.com
Rita is a resident paw expert at Pet Keepers. A registered & licensed dog trainer, she also has a degree in animal nutrition, and runs her own dog training course.

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