In this video, we go through the Seven Deadly Aquarium Sins — the mistakes beginners make that silently destroy fish, plants, shrimp, filters, and sanity.
Each “sin” is explained in a medieval-inspired way, but the advice is practical, simple, and actually useful if you’re new to the hobby.

Whether you’re setting up your first tank or already knee-deep in water changes, this guide will help you avoid the most common (and most avoidable) problems in fishkeeping.

In this video:

Forgive me, fish father, for I have sinned — on accident, of course. I’ve made some biblical mistakes when I was starting out. So, in order to save my beginner brethren, I’ve made some important revisions to the original cardinal sins to guide you to aquarium salvation.

These are the Seven Deadly Aquarium Sins beginners need to know.

Sin No. 1 — Aquasoil Lust

Beginners will look at our store display tanks and start frothing at the mouth over how pretty our plants are. Deep in their lust for the pretty, pretty stem plants, they assume theirs isn’t doing too well because they have gravel.

They then grab a bag of Amazonia and go home in a sweat… to commit murder.

The next morning, after adding soil, they go to feed Benjamin and Sally only to find a crime scene of upside-down fish. What happened?

Well, they fell for aquasoil’s sexy, sexy tricks.

A lot of aquarium soils leach ammonia for the first few weeks. It wipes out your beneficial bacteria and kills your fish.

The Solution

If you want to change substrates, treat it like any good relationship — take it slow.

Remove a handful of gravel
Replace with a handful of soil
Do this every two weeks

A handful won’t crash your tank, but it will spike your ammonia and soften your water. Treat each addition like a mini cycle:

30% water change twice in the first week
40% water change the following week
Repeat
Test ammonia regularly
If it’s above 0.25 ppm → water change, water change, water change

Water changes cleanse the soul.
This gentle “soil edging” keeps your lust under control — and your fish alive.

Sin No. 2 — Cleaning Wrath

A couple of weeks after setup, aquariums go through puberty. They get pimples in the form of algae, detritus, and weird-looking films.

Beginners, in an aggressive attempt to save their tank, will:

drain everything
scrub every surface with tap water
polish every grain of gravel
rinse the filter under the tap
chuck it all back in before dinner

Welcome, dear beginners, to aquarium purgatory.

Your impatience and anger have trapped you in a loop of restarting the cycle every time you clean it.

The Solution

Clean your filter and substrate with aquarium water, not tap water — especially in the early weeks.

Treat your substrate and filter as separate colonies. Clean them on different days, for example:

Filter on Wednesday
Water change and substrate vacuum on Sunday

This allows the stronger bacterial colony to defend the realm while the other rebuilds.

Sin No. 3 — The Gluttony Killings

There is one common practice I’ve witnessed as plant manager in Australia’s largest aquarium store, and that is:

killing your aquarium plants… then buying more.

A true horticultural massacre.

Newcomers swear they “can’t afford a $150 light,” yet somehow restock their lamp-lit medieval dungeon tank four or five times. By the end, they’ve spent more than the cost of a proper setup and have nothing but dead plants to show for it.

They are then ready to accept the prophecy:
A powerful LED with proper white, red, green, and blue channels will:

save you money
save your plants
save your sanity

Plants, unlike fish, don’t scream. So beginners commit unspeakable botanical sins without guilt.

You’ve got to listen to your plants, man. They’re trying to tell you something.

Sin No. 4 — The Greedy MTS (Multiple Tank Syndrome)

This transgression is one of the most powerful forces in the entire hobby — a temptation so strong it deserves scientific study.

A beginner never understands what they’re up against until they have their first hit.
One tank… and suddenly they’re chasing the dragon.

You need more tanks, more fish, more excuses.
“It was free on Marketplace!”

That’s how it starts.

Then you blink and suddenly you’re five tanks deep, the high doesn’t hit the same, but now you’ve got mouths to feed. Plants are overgrowing, algae is invading your soul, and your parents are yelling at you because the power bill spiked — and you can’t blame the economy anymore.

This causes the crash-out:

water changes skipped
fish getting sick
maintenance drowning you

Yes, fish-keeping sickness is real. Unfortunately, there is no cure. It’s a rite of passage.

You have been warned.

Sin No. 5 — Maintenance Sloth

It’s painfully easy to catch a heavy case of the CBFs once the novelty wears off.

Let’s be honest — at Nature Pets we run more than 15 tanks with full-time staff, and even then it’s easy to fall behind. So don’t beat yourself up. If a whole team can fall behind, a lone hobbyist never stood a chance.

The Cure

Limit how many tanks you own, then make your work easier:

Use a siphon instead of scooping
A magnetic scraper is quicker and less involved
Keep gear accessible and organised to silence the procrastination demon
And if all else fails… recruit a gullible loved one into your crusade

Sin No. 6 — Shrimp Envy

It’s super easy to feel envious of shrimp keepers online with their perfect thriving colonies, especially when you’ve only got three survivors and a mysterious population decline that even priests can’t explain.

This is usually because you’re making regular sacrifices to the evil filter overlord.

Baby shrimp are tiny, and if you run a hang-on-back, canister, or internal filter, they’re probably getting sucked through the outlet and turned into chunky shrimp salsa.

Protection

For HOB or canisters → cover the intake with a large sponge and reduce flow
For internal filters → replace the coarse sponge with fine wool to block grates
For shrimp-only tanks → abandon the overlord entirely and convert to a sponge filter

Sponge filters are the holy safeguard of shrimp tanks.

Sin No. 7 — The Proud Keeper

I have witnessed fully grown adults claim to be experienced fish keepers, then show me photos of:

an adult flowerhorn in a 40-litre tank, or
neon tetras labelled as “cold-water fish” because “they don’t need a heater”

When pride gets in the way of advice from people who do this for a living, fish usually die.

And although there are rare anomalies — bettas thriving in community tanks, etc. — the general rules exist for a reason.

The moment you let pride convince you that your one experience is divine truth, and you start insulting people online over it… you’ve lost, buddy.

Being a lifelong student and remembering that:

every tank is different
every ecosystem has its own personality disorder
every person starts somewhere

…is the best thing you can do for this community.

Hold on to that and you’ll keep your fish alive, your plants thriving, and your For You Page positive — which in this hobby is as close to a miracle as you’ll get.

Final Thoughts

These are the Seven Deadly Sins of aquarium keeping.
I’ve written these to keep you from meeting Cthulhu face-to-face in the fiery depths of aquarium hell.

And if you’ve committed any of these…
you must repent immediately by clicking subscribe.

Your sins will be washed away.
Probably.

Thanks for watching.