1.2. Falsehoods and Myths in the Aquarium Hobby

There are many dogmas, myths, misconceptions, misbeliefs, falsehoods, and phony religions promulgated in keeping tropical aquariums. Most are someone’s opinion that one thing or another is going to damage the tropical fish and one shouldn’t do it (whatever it is). This sort of negative naysaying is very easy to do and often very difficult to disprove since it is often difficult to prove there is not a certain set of circumstances where the naysayer is correct. It is called proving a negative and is a known statistical problem.

Most of these myths can be determined to be false simply with a little common sense. Scientists in universities researching topics for aquaculture or the home aquarium have refuted still more of these naysayer ideas as unfounded. We have accumulated a list of 150 falsehoods and linked these falsehoods to the specific article on this website addressing said myth.

We give this list of 150 myths twice: once just as a list, and a second time with links to the articles debunking the myth. The list of myths is:

The brown “gunk” inside the filter bio-media or filter foam is trapped feces and it is beneficial to the aquarium to remove it frequently and thoroughly. (This is by far the biggest and most damaging myth)
Stability in aquarium parameters (temperature, pH, hardness) over seconds, minutes, hours, or days is important. (The howls of protest over even suggesting this a myth will be heard for miles)
Nitrates going above 10, 20, 40, or even 80 ppm will shorten the life of an adult fish.
Testing water parameters is essential to diagnosing fish diseases.
The type of food fed to fish is directly critical to success in the hobby.
At least 25% of water changes should be done once a week, with 50% weekly being recommended.
Under-gravel filters don’t work well.
Hang-on-back cartridge filters are filters that give great biological filtration.
Most canister filters filled with the media that comes with them (typically ceramic rings and bio-balls) are great biological filters.
As long as the filtration is adequate to oxidize ammonia, more filtration will not help the health of the fish.
“Overstocking” a fish aquarium will shorten the life of a fish.
Tropical fish thrive in water conditions outside what occurs in their native waters because they have been bred in captivity.
Mixing fish species from different continents or different biotopes will shorten the life of the fish.
A fish can appear healthy and fine but not be “thriving”.
Ammonia levels at some level below 5 ppm or nitrite levels below 1 ppm are detrimental in any way to fish at a pH of 7.
Ammonia levels at 5 to 10 ppm or nitrite levels at 1 ppm to 5 pm are very toxic to fish at a pH of 7.
Ich is a horrible disease that will kill most of the fish infected with it.
Raising the aquarium temperature is an effective way to treat ich.
It’s dangerous to the fish to “chase” pH with chemicals.
High pH (>7.5 pH) is dropped by using organic materials such as almond leaves, beech leaves, oak leaves, peat, and/or driftwood.
Fish will have their lives shortened if put in a pH different than their native waters.
Fish from the Blackwater Amazon will suffer in water with a high pH.
The hardness (GH) of the water is important to juvenile and adult fish
Dropping a fish into the water with a different pH or temperature will “shock” it and can kill it.
If one lowers phosphates in the water, algae will go away
Temperatures need to be closely held for healthy fish
Heaters are an absolute necessity in most homes.
Each fish has a minimum aquarium size and length beyond being large enough to swim freely in.
Fish in an aquarium that is too small will not grow to their full size, other than goldfish.
It is “cruel” to keep fish in aquariums less than twenty gallons in size.
Different types of fish (herbivores, carnivores) can’t be kept together because they require different foods.
Beneficial bacteria only exist in thin very adherent biofilms on filter media and substrate, not in the soft brown “gunk” on the filter which can be washed off or vacuumed out.
Beneficial bacteria only multiply to the number they have at the end of cycling.
Adding a lot of fish to an established aquarium is dangerous as the beneficial bacteria cannot increase their load rapidly.
High protein fish food is directly bad for fish
The only type of beneficial aerobic bacteria found on the surfaces of a filter are the bacteria that oxidize ammonia to nitrate.
Filters should be cleaned at least every month.
Filters and sponges must be cleaned in aquarium water and never in chlorinated water.
The larger the filter the fewer nitrates in an aquarium and the fewer water changes required.
Water that has been run through a water softener is bad for fish.
Water changes remove built-up toxins, heavy metals, and fish hormones in the water.
Water changes are bad because they cause variation in the water parameters.
Frequent water changes help cure fish diseases.
Have one gallon of water for every inch of fish.
Feed fish only what they can consume in five minutes.
There are bad types of filters called “nitrate factories”.
Under-gravel filters need lots of maintenance.
Only the flow rate in gallons per hour determines filter efficiency, not square feet of bio-media surface.
A canister that has an actual flow rate of 600 GPH (gallons per hour) can filter roughly twice the amount of fish that a canister that has an actual flow rate of 300 GPH.
When shipped fish are un-bagged, they should be gradually acclimated to their new water chemistry.
If fish get red blotches on their skin and fins in an aquarium it is generally something called “ammonia burn”, not bacterial hemorrhagic septicemia.
Anaerobic or anoxic (very low or no oxygen) conditions can occur in a normal aquarium.
Poisonous gas can form in the aquarium
Poisonous gas pockets form in the sand if it is not mixed occasionally
“Seeding” a new aquarium with “gunk” from an old established aquarium spreads disease.
If nitrite levels are over 9 ppm in a cycling aquarium the beneficial bacterial growth is inhibited
If ammonia levels are over 4 ppm in a cycling aquarium the beneficial bacterial growth will be inhibited.
If moderate amounts of fish are added to an aquarium that isn’t cycled, a good percentage of the time the fish will die.
It is best to start with an aquarium that has a moderate number of fish and a moderate amount of plants in it.
Too much protein causes Malawi Bloat in mbuna
Bloodworms are too rich for fish and will cause bloat.
Malawi cichlids can over-engorge on tubifex, giving the fish bloat.
Tubifex worms can carry a parasite that can infect tropical fish.
The saturated fats in mammalian meat are bad for fish.
Beef heart causes intestinal obstructions in fish.
Any land animal or warm-blooded animal produces a protein that cannot be digested by fish.
Fat from warm-blooded animals will cause the death of fish.
High-fat foods can kill the fish.
Fish food with ingredients like “chicken byproducts” is bad food for fish.
Krill is not as good in fish food as fish meal.
If you feed feeder fish like goldfish which have high levels of thiaminase enzyme your fish will get sick or die.
Freeze-dried food will expand in the stomach of the fish and cause bloat.
Fish should never be fed cold or frozen food.
If a book or website recommends fish food or tells you a fish food to avoid one can believe it.
“Fish meal” is an ingredient in poor quality fish food.
The ingredients list on commercial fish food is based on wet weight and thus inaccurate.
Krill protein is superior to all other proteins.
Whole fish meal is superior to fish meal.
Tilapia filets have no nutritional value.
Plant protein is superior nutritionally over animal protein.
Feeder fish don’t carry disease and are thus a safe fish food.
“Just like us, fish enjoy a varied diet”.
Vitamin supplements are a good idea with fish.
There is such a thing as “high quality” and “low quality” animal protein.
Mbuna are herbivores and eat only plants.
Fish will starve before eating a fish food they don’t “like”.
Substrates and decorations act as biofilters.
Gravel substrates should be frequently cleaned of all the horrid brown gunk that accumulates.
If you drop vinegar or acid on a rock and it bubbles, the rock cannot be used in the aquarium.
Never put a rock in your aquarium without knowing the composition as many minerals in rocks are poisonous to fish.
Some tumbled polished rocks and some gemstones are poisonous in an aquarium
Geodes and crystals need to never be put in an aquarium as they can be poisonous.
Avoid any rocks with sparkles in them as they can be poisonous.
Heavy metals can be present in rocks and will leach out and kill your fish
Avoid all rocks that have “veins of metal” in them as they will poison your fish.
All metal should be avoided in the aquarium as it will oxidize and kill your fish.
Sharp rocks and substrates can cut and harm the fish.
Always clean rocks thoroughly as they might have insecticides or herbicides on them.
Always boil rocks before putting them in an aquarium to kill all pathogens.
Never boil rocks as they can explode.
Sandstone and shales need to be avoided as aquarium rocks as they will fall apart.
Porous rocks should be cleaned with a detergent before putting them in an aquarium.
Green rocks will leach copper and kill your shrimp and fish.
Do not use shells and coral as ornaments in an aquarium as they will create bad water chemistry in the aquarium.
Bone and antlers will decompose if not coated.
Avoid rocks from the seashore as they might contain too much salt.
High silica rocks like quartz in a rock substrate will leach silica and cause diatom blooms
Do not use wood as a decoration in your aquarium without knowing what tree it comes from as some wood is poisonous.
Do not use wood as a decoration in your aquarium without boiling it to kill all pathogens.
Wood in an aquarium can significantly drop the pH.
Driftwood from the ocean shouldn’t be used as decoration in an aquarium as it could contain a lot of salt.
Be careful with wood you find as it might be contaminated with insecticides or herbicides.
You can remove the tannins in wood by soaking them for a few weeks or boiling them.
If you boil wood it will sink in an aquarium.
All wood should be sterilized with bleach before putting it in an aquarium.
Decomposing wood can cause an ammonia, nitrite, or nitrate spike.
Only hardwoods are suitable for aquarium decorations.
Since UV units don’t filter, they can’t give crystal-clear water.
Aquarium UV units require one watt of power for every gallon of aquarium water to kill ich and other tough to kill pathogens.
Aquarium UV units require decent water residence times in the units to be effective.
If the food supply of beneficial bacteria is cut off, they die in a matter of hours or days.
Oxygenation of the water before the filter is useless as the bacteria in the filter will remove the oxygen.
There are anaerobic nitrate removing reactor designs commercially available that work well in the aquarium.
“White-eyes” is due to water quality issues.
Neons are an easy fish that is good for a new tank.
Plecos require wood in their diet.
Goldfish don’t thrive in warm water aquariums.
Common, comet, fantail, Sarasa, and shubunkin goldfish are not fish for beginners.
Goldfish need at least twenty to thirty to forty to fifty gallons (depending on the “expert”) per fish.
Goldfish in a small aquarium stop growing but their organs continue to grow and they die an early death.
Lots of bacteria in the water always results in cloudy water.
The use of “chemicals” such as metronidazole, praziquantel, and antibiotics to treat fish diseases should be avoided as they will probably kill the fish.
Fish absorb medicines through their skin and gills.
Freshwater fish drink the water they swim in so putting medicine into the water gets the medicine into the fish.
Salt (sodium chloride) added to the aquarium assists in the healing of injuries, promotes the formation of slime coating, and improves gill function.
Using antibiotics in the home aquarium will result in antibiotic-resistant bacteria.
It is beneficial to have more than one type of biofiltration media as each type of media has its strong points.
Foam in a canister is a mechanical filter and is a poor biological filter.
Aquarium gravel is not a useful media for biofiltration in canisters and sumps.
Lava rock is a great biological filtration media.
“K1” extruded plastic media is only useful in fluidized beds and is not a good biomedia for submerged static media beds.
“K1” fluidized beds take longer to cycle than standard submerged beds.
“K1” fluidized beds are not as efficient as submerged static media beds.
Trickle filters are very efficient filters.
Wet/dry filters are very good efficient filters.
Corydoras and tetras are very sensitive to salt in the water
Fish eat prefer food that has garlic in it
Livebearers such as Mollies, guppies, platies, and swordtails require hard water, salt, and/or alkaline pH.
Bacterial blooms are composed of beneficial bacteria in the water column.
Sharp gravel will destroy the barbels of corydoras and loaches

These are ALL untrue myths

Links to Debunk the Myths

These myths and falsehoods are repeated below with links to the articles on this website that debunk the myth:

Note that this list only includes those myths which are repeated many times from well-intentioned commentators on social media. If this list included all the falsehoods seen on social media from obvious newbies to the hobby the list would be in the several hundred. For instance, the a common misconception that beneficial bacteria are present in “old” aquarium water. There are tiny numbers of beneficial bacteria in “old” aquarium water but the numbers won’t jump-start a cycle.

Most of these myths are just overly-cautious opinions unsupported by any objective scientific research (and often contradicted by the real research!). If one follows all the “rules” from the well meaning but ill-informed commentators on social media a hobbyist will have to spend enormous amounts of time and money keeping up their aquariums. Keeping beautiful aquariums doesn’t have to be expensive and time-consuming. Mother Nature is very flexible and very forgiving.

The Semmelweis Reflex

Note that we can state with absolute certainty that everyone and we mean EVERYONE, who reads this list will have at least ten myths and probably more like twenty to thirty myths where they said “NO!! THAT’S NOT A MYTH!! THAT’S TRUE!!! IF YOU DON’T FOLLOW THIS YOUR FISH CAN DIE!!!”

And they will maintain that belief even when presented with five or more university papers or solid experimental evidence saying it is a myth. They will rationalize and rationalize some more and reject the scientific evidence.

This is the psychological phenomenon called the “Semmelweis reflex”. The “Semmelweis reflex” is a metaphor for the reflex-like tendency to reject new evidence or new knowledge because it contradicts established norms, beliefs, or paradigms. This is something which EVERYONE does and is simply a fact of life that we can’t and won’t try to overcome.

Most of the self proclaimed “aquarium experts” and “old dogs” who read this list will come out on social media and say this list is just plain dangerous. But of course, they obviously never read the supporting links about the myths they have issues with. Good old “ignorance is bliss” personified.

“The good thing about science is that it’s true whether or not you believe in it.”

Neil deGrasse Tyson

I have noticed an interesting twist. The longer someone has been involved with the hobby the more ingrained these myths become. While newcomers to the hobby seem to be very accepting that these 150 items are all myths, the “gurus” and “old dogs” are unanimous that most of the list is complete garbage. Interesting!

Nannostomus mortenthaleri Red Pencilfish — Nannostomus Morgenthaler Red Pencilfish

There is another category of 25 falsehoods that are covered under a separate section:

1.3. False Marketing Claims

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