15 Aquarium Myths Busted

Read Time: 8 mins

1. Fish grow to the size of their tanks

If you pay attention to nothing else in this article, please understand: this is not how it works. It doesn't work for reptiles or amphibians, either. It doesn't work with any living thing.

Imagine if we tried this with other animals.
"No, we keep our Great Dane in a kennel. He's going to stay the size of a Shi Tzu."
"I live in half of a studio apartment. I'm going to stay under 5'3 and my friend who lives in a 3 bedroom is going to be in the NBA."

If that sounds ridiculous, so should keeping an Oscar in a 5 gallon cube and expecting it to go well. The best I can figure for how this got started is fish kept in a less than optimal environment didn't grow well due to stress, or they died small and young because their tank couldn't support them and folks ran with it.

2. A smaller aquarium is easier and more beginner friendly

This one is so common and deceptively simple we did a whole post on it (here's that blog if you wanna check it out). The TLDR of the post is a smaller aquarium may feel like less of a commitment or investment, but it is easier to change for the worse and make mistakes with.

More water acts like a kind of safety net for rookie mistakes like overfeeding, cycling errors, etc. because larger volumes of water are harder to change.

3. "If you're not sure what to put in a tank, go by 1" of fish per gallon of water!"

I've seen this one perpetuated even by well-respected sources, but it's not nuanced enough to be useful to folks new to stocking tanks. 

This statement doesn't take into account fish growth and behavior patterns or tank dimensions. All gallons aren't created equal. A 20 gallon long aquarium is often roomier than a 30 gallon vertical aquarium to your fish because it has a larger footprint. 

4. Fish are cheap and easy pets

This one can be partially true depending on what you're talking about. There are some fish and aquarium plant species you can get for a couple bucks and that could probably survive having gasoline poured in the tank (hyperbolic - please don't fuel your fish. They get into enough trouble without internal combustion).

Unfortunately, though, it's no secret aquariums can be an expensive hobby. Fish themselves can be cheap, but a 55 gallon tank right now is running at around $160 - $200 or more at larger pet store chains, and that's just for the tank, not including heaters, stands, lights, plants, etc. Even the price of smaller tanks continues to rise.

There's a huge number of variables determining the initial cost of your tank, so to say fish are cheap and easy is too simplistic if you want a healthy aquarium.

Maintenance doesn't have to be pricey, though, and there are ways to cut costs without negatively affecting your fish. Check back in soon for a new post on how to make aquariums more budget friendly!

5. My tank doesn't look like such-and-such's tank so I must be doing something wrong OR "That person's tank looks amazing; they must know what they're doing and I should mimic exactly what they do"

The gist is this: aquariums are mini ecosystems, and every single hobbyist has different goals with different strategies that work best for them. You cannot exactly replicate someone else's tank. And just because something works for someone else doesn't mean it'll work for you. 

On that note, just because someone's tank happens to look good doesn't mean they're following sound practices to get there.

If you want a cool-looking aquarium with a few plants for a bit of green, your maintenance needs are going to be vastly different from someone trying to run a lush, jungle show tank. Different fish and plant species have different needs, tap water chemistry is vastly different across the world, and availability of materials varies hugely depending on your area.

I used to work with someone who kept adding minerals to her water to increase her plant growth because another hobbyist across the country did it that way, and she couldn't figure out why her water chemistry was always weird. We live in KY, which has some of the hardest tap water in the country. She was overdosing calcium and magnesium. I used to think I needed to fertilize more heavily than I do now because of the schedules you see posted online, but turns out, my setup didn't need that much. 

Basically, there are scientific principles that hold true regardless of what setup you're running, but those can be applied a thousand different ways based on your needs. 

6. Changing the water/filter really often keeps your tank cleaner (see also: I should take out as much water as possible during water changes so it'll "last longer")

Huge changes quickly in an aquarium are never the way to go. While it seems counterintuitive, if you maintain your tank this way, you're just doing extra work for nothing. 

Making massive water changes can disrupt your tank's nitrogen cycle, stress more sensitive fish species, or negatively impact your beneficial bacteria populations. Drastic water changes should only be done in specific circumstances, such as if a harmful chemical was accidentally added to a tank and so on. 

7. Goldfish, Bettas, insert-other-rabidly-misunderstood-species-here can live in a bowl or a cube on my desk

Bettas and goldfish seriously have some of the worst lived in the pet trade. Though these species are often kept in smaller containers in pet stores for ease of care, it's meant to be a temporary solution, not something you should emulate. 

For more myths and misconceptions about keeping bettas specifically, check out this blog post! 

8. Fish breathe the oxygen in H2O, so I don't need to worry about making sure my tank has enough oxygen

Many folks assume fish gills work like little oxygen vacuums that pull the oxygen from the two hydrogens in the water molecule. However, as cool as that would be to watch in real time, that's not how it happens. That oxygen stays bound to hydrogen as water.

Fish actually breathe atmospheric oxygen like we do dissolved in the water column (AKA dissolved oxygen/DO). So it's important to keep your tank water from sitting too still by providing adequate aeration, mostly in the form of water surface agitation via filters, airstones/air pumps, spray bars, etc. 

9. Related to #8: Airstones produce dissolved oxygen and can replace surface agitation to provide DO

This one is a little more sciencey. Airstones help with the introduction and circulation of dissolved oxygen, but the bubbles they make produce very little oxygen on their own your fish can use. Airstones are a useful tool! Don't get us wrong; we swear by them. This isn't to say airstones aren't effective at increasing oxygen levels. But it's the circulation and turbulence these devices help create that can increase the oxygen in your tank, not the actual bubbles. This is why finding the right place for your airstone in your tank is important to ensure gas gets circulated efficiently. 

Oxygen is absorbed into the water column primarily from the atmosphere at the water's surface. Based on U.S. Fish and Wildlife data, in areas where water is more turbulent, dissolved oxygen is higher. So, the airstone itself doesn't produce O2, but instead allows more O2 to enter the water at the surface. For this reason, airstones can be especially useful if you have a tall/vertical tank with less surface area for gas exchange. 

10. You can just flush dead (or unwanted living) fish

Aside from being a really undignified way to get rid of a pet, it's not good for the environment or your plumbing. 

If you flush a living fish, it goes one of two ways, and neither are good. One, the fish dies inhumanely in the sewer system. Two, it miraculously survives water processing and finds its way into natural waterways, where it can cause massive biological problems as an invasive species (the odds of a fish's making it this far are extremely slim, but listen, we saw fire tornados and death wasps in 2020. I'm not taking chances). On that note, never release your fish into the wild to get rid of it, either. Ditto for your aquarium plants. 

If you flush a dead fish, you run the risk of plumbing issues or causing problems for water processing systems. The fish could also get stuck in your plumbing and create a pocket for disease and parasites. 

11. You can introduce new fish to a tank straight away and/or instant cycle a tank

This one is usually perpetuated by someone who's selling something. Yes, there are water additives that can help shorten cycling time and more rapidly increase beneficial bacteria, but you cannot cycle a tank overnight. You just can't. The microbiome of a healthy tank takes a while to fully establish. Therefore, you can't add fish immediately after setting up your tank. Some sources discuss fish-in cycling, but it puts unnecessary stress on your fish. 

Similarly, you also can't introduce fish to a cycled tank instantly. They need time to adjust to the change in water temperature, chemistry, etc. and should be transitioned slowly to avoid shock. And if you're adding them to a tank that already has fish, quarantining is the best practice. 

When dealing with living things, simplistically stated, fast change is rarely good change.

12. My plants are turning yellow/dying/other symptom; they must need fertilizer

It's possible they do, but people too often immediately jump to fertilizing when they see plant problems instead of confirming nutrients were the issue. It's easy to nitpick and focus on exactly how much of a particular nutrient you're supplying, but there are dozens of other more common factors that could cause plant issues.

Light, destructive tank inhabitants, algae, incorrect planting, lack of oxygenation, even natural plant life cycles could be the cause for the change in your plants' appearance.

To tag onto this with a related myth, adding fertilizer won't immediately fix your plants even if you do have a nutrient deficiency. Plants respond to changes slowly. 

13. Too many plants will suck all the oxygen out of my tank at night and suffocate my fish, so I shouldn't plant too heavily

Even if you have a high plant load, it's not gonna happen if you have adequate aeration. Same holds if you have a bunch of house plants in your bedroom or in a hospital room (apparently there's a myth that having plants in a patient's room will siphon their last breaths or something. I don't know how that got started).

While it's true during the evening, plants respire (using oxygen and producing CO2, the opposite of what they do during photosynthesis) the changes in oxygen concentration are barely noticeable. If you see signs of hypoxia (fish gasping at the water surface, etc.), chances are it's not because of your plants. 

HOWEVER: if you have heavy floating plants, there may be less room for surface gas exchange, and this can impact your oxygen levels. So keep that in mind when coming up with aeration strategies. 

14. I have algae. My tank is dirty, I'm doing something wrong, and it's going to hurt my fish. All algae is the devil.

You're blasting an enclosed glass box with light, heat, and nutrients. Of course you're likely to see some algae. 

First off, algae is not harmful to your fish unless you have such a large amount it's blocking healthy gas exchange. A little bit of algae won't hurt your fish at all. Secondly, just given the nature of aquariums, it's extremely unlikely you won't encounter algae even if you have the most perfectly maintained aquarium on the planet. 

As long as you are adequately controlling algae growth and the causes for algae growth, seeing some here and there isn't indicative you're horrible at aquariums. 

Here's an in-depth article on algae for those who might be dealing with it. 

15. I need to feed my fish multiple times a day, every day. After all, I eat three meals a day, so won't they be hungry if they don't?

Overfeeding is one of the biggest causes of out-of-whack water parameters in the hobby. It also can cause health problems like bloat for your fish. Fish don't need to eat as often as we do; they evolved differently than humans. You should only ever feed as much as your specific fish species needs, and do your best to remove the excess to avoid problems like ammonia spikes.

Got more myths you want us to cover? Hit us up, and tank on!