Some fish look harmless in the store… until they grow up and turn your peaceful planted tank into a stress arena. In this video, I break down five popular species that beginners should avoid — not because they’re “bad fish,” but because their behaviour, size, or care needs clash hard with what most new hobbyists are prepared for.
We’re talking slime-coat snackers, undercover fin-nippers, living bulldozers, and fish that outgrow the dream tank you thought would last years. I’ll explain what actually goes wrong, what to expect as they mature, and which alternatives make life a whole lot easier.
If you’re planning your first aquarium and want a tank that thrives instead of turning into a battleground, this will point you in the right direction.
In this video:
There are soft, gentle, peaceful fish.
And then there are absolute bullies.
They nip, chase, take over, and wreak havoc if you don’t know what you’re doing. And while some look like absolute orcs raised by Saruman, others can slip through the bully radar — especially if you’re new.
All fish have their rightful place within the aquarium world. But today we’ll be looking at five fish that beginners should completely avoid if they want to have an absolute banger of a tropical tank.
5. Silver Shark (Bala Shark)
There’s something in the male genome that activates at the word shark. Doesn’t matter that silver sharks aren’t sharks — say the word and you’ll bring beginner boys to the yard.
Silver sharks are the perfect example of why you should never judge a fish by its size at the aquarium store. They start out small, cute, and sleek — the perfect gateway fish for someone thinking, “I want something badass but also affordable.”
But don’t be fooled by their juvenile size.
Silver sharks grow fast, and they grow huge. Within a couple of years they can reach 35 cm long.
And it’s not just their size that’s the problem:
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They are social fish and should be kept in groups of at least six.
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Six foot-long fish means a minimum tank size of around 400 litres.
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They’re opportunistic feeders, meaning anything that fits in their mouth becomes a snack.
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They’re skittish and known to launch themselves out of tanks.
Silver sharks are incredible fish — but far better suited to large specialist setups, not beginners still learning the basics. They scratch that childhood apex-predator itch, but they are monsters, and they require a monster tank to match.
4. Tiger Barbs
Tiger barbs are the masters of identity fraud in the aquarium world.
They school beautifully, explore the tank with confidence, and blend in so well you’d swear they were perfect for a community setup.
But tiger barbs are known for one thing:
Opportunistic fin-nipping.
Tiger barbs are cardio machines. They chase relentlessly, circling tankmates with the same energy as a kid who’s had 17 Red Bulls. This results in stressed, exhausted fish who end up with missing chunks of fins — and dignity.
Fin-nipping opens the door to infections, stress, and sometimes death if it gets bad enough.
To make matters worse, tiger barbs become territorial as they age. Community tanks quickly divide into zones the barbs aggressively patrol — and they take their jobs way too seriously.
If you want something similar, look at Five-Banded Barbs. They’re far less aggressive but still look and feel like tiger barbs without all the shady dealings.
3. Goldfish
Goldfish are the most misunderstood fish in the hobby.
They’re iconic, well-known, and assumed to be the easiest to keep — which couldn’t be further from the truth.
Goldfish have stunning colours and bold personalities, so it’s easy to see why they’ve been a favourite for generations. But despite all this, goldfish are not beginner-friendly.
Size myths and stunting
It’s a myth that goldfish only grow to the size of their tank.
Slim-bodied goldfish like comets or shubunkins can reach 30 cm long. If they don’t, it’s due to stunted growth from being kept in an aquarium that’s too small — and they really should be rehomed into a pond.
Messy feeders
Goldfish are messy eaters and produce a huge amount of waste, leading to harmful ammonia spikes. Strong filtration and frequent maintenance are essential — which removes the “fun” for many beginners.
Cold-water limitations
They’re cold-water fish, meaning you can’t mix them with tropical species, and they completely destroy plants, making planted tanks impossible.
On their own, goldfish can be wonderful pets. But if you want a lush planted tank with variety and colour, goldfish are not the guy.
2. Oscars
A lot of people say they prefer personality over looks — but with Oscars, congratulations, you get both.
Oscars are the equivalent of a wet puppy. Sounds great on paper, but there’s something more sinister beneath their good looks and boisterous personality.
Like puppies, Oscars grow up. And although they won’t chew your couch, they’ll absolutely chew any fish smaller than them.
Their huge size also means they poop a lot, which requires frequent water changes. You also can’t rely on plants to help with waste because Oscars will simply destroy them.
They dig, uproot, spit, chew, and shred — not because they’re herbivores, but because chaos is their hobby.
If you want a fish full of personality without the enormous tank size, choose a betta. They have attitude but only need around 60 litres, and you can usually keep a small school of tetras with them — plus they won’t annihilate your plants.
1. Cichlids
Cichlids are well known for their territorial and aggressive behaviours, but beginners often buy them thinking they’re just big, colourful fish.
What they don’t realise is that with cichlids, you either keep one, or you keep a lot.
There is no in-between.
The in-between is where the murder happens.
Their social structure relies heavily on hierarchy, territorial boundaries, and environmental complexity. These species can only be kept successfully as:
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a single specimen, or
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a large group where aggression is spread out.
Keeping two or three usually results in one fish being relentlessly bullied.
Successful cichlid tanks require carefully constructed hardscape — rocks, caves, line-of-sight breaks — which can be difficult for beginners to build correctly. Without this balance, cichlids will chase, injure, or kill weaker tankmates and quickly dominate the aquarium.
For something colourful, interactive, and far more manageable, Apistogramma species are a fantastic alternative. They offer similar personality and visual appeal without the high aggression.
Final Thoughts
These are the five fish I would not recommend for beginners.
At the end of the day, choosing the right fish is about knowing yourself as much as the species. If your lifestyle says, “I want a peaceful little kingdom that runs itself,” then don’t summon creatures that require constant care, side missions, and emotional labour.
Beginners get caught when they choose with their eyes instead of their reality, because wanting the dragon may bring the fire.
Put your lifestyle above your fish fantasies, and you’ll build a tropical planted realm that thrives instead of becoming a battleground.
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Thanks for watching.
