In recent years, with the rise of short videos, many people have watched fish-keeping influencers easily maintain beautiful aquariums full of vibrant fish. This has inspired countless beginners to start their own fish-keeping journey.
Unfortunately, almost every beginner makes the same five mistakes, leading to countless dead fish before they even get the basics right.
In this article, we’ll go over the five most common mistakes beginner fish keepers make and how to avoid them — so you can build confidence and keep your fish healthy and alive.
Mistake 1: Putting Fish Directly into a New Tank
Many beginners buy fish and an aquarium, then immediately add the fish into the tank without any preparation.
What they don’t realize is that a lot needs to be done before introducing fish. Anyone with basic fish-keeping knowledge knows that the most important first step is to establish a nitrogen cycle (nitrification system) in the tank.
Without this system, fish waste quickly produces toxic ammonia and nitrites, which can easily poison and kill the fish. In short — no established cycle, no surviving fish.
Mistake 2: Buying Every Fish You Like and Mixing Them All Together
Many beginners buy every fish they find attractive, putting them all in one aquarium regardless of size or species.
The result? A chaotic tank full of fights, injuries, and even big fish eating smaller fish.
As the number of fish increases, the tank’s oxygen and filtration system become overloaded. Poor water quality follows, leading to stress, disease, and eventually mass fish deaths.
In fish keeping, less is often more.
Mistake 3: Overfeeding Out of Love
New fish keepers often overfeed because they’re afraid their fish might be hungry. Every time they pass by the tank, they toss in more food — sometimes a handful at once.
But overfeeding is one of the biggest causes of fish death. Uneaten food quickly decomposes and pollutes the water, creating toxic conditions.
Meanwhile, fish that eat too much can develop digestive problems or swim bladder issues, both of which can be fatal. Feeding small amounts two to three times a day is much safer than constant overfeeding.
Mistake 4: Not Changing Water (or Changing It Too Often)
Beginners often make one of two extreme mistakes when it comes to water changes — either never changing the water, or changing it too frequently.
Both are harmful.
If you never change the water, toxins and waste accumulate, hurting your fish.
If you change the water too often, the tank’s ecosystem loses stability, stressing the fish and potentially causing illness.
The key is balance — partial water changes (about 20–30%) once a week usually keep the aquarium healthy and stable.
Mistake 5: Overusing Salt and Medication
Many beginners panic at the first sign of trouble — cloudy water, fish scratching, or odd swimming behavior — and immediately start adding salt or medication.
However, both salt and medicine can be harmful when used unnecessarily or excessively. Overuse can disrupt the biological balance and worsen the water quality, killing more fish instead of saving them.
It’s always best to identify the real problem first, test your water parameters, and use treatments only when truly needed.
Final Thoughts
So, have you ever made one of these five common fish-keeping mistakes?
Don’t worry — every aquarist starts somewhere. By learning from these pitfalls and taking the time to understand your aquarium’s ecosystem, you can keep your fish healthy, happy, and thriving.
