15 Aquarium Myths Debunked: Stop Believing These

Why Myths Persist in the Hobby
Myth 1: Fish Grow to the Size of Their Tank
Myth 2: Goldfish Bowls Are Fine
Myth 3: Bettas Like Small Spaces
Myth 4: Wait 24 Hours After Adding Conditioner
Myth 5: Algae Means Your Tank Is Dirty
Myth 6: Snails Are Always Bad
Myth 7: More Filtration Means Fewer Water Changes
Myth 8: Fish Have a Three-Second Memory
Myth 9: Aquarium Salt Cures Everything
Myth 10: You Need a Heater in Singapore
Myth 11: Bubbles Equal Oxygen
Myth 12: Gravel Is Better Than Sand
Myth 13: Leave Lights on 12+ Hours for Plants
Myth 14: Bigger Fish Always Eat Smaller Fish
Myth 15: You Cannot Overfilter a Tank
Frequently Asked Questions

Why Myths Persist in the Hobby

Aquarium keeping has been a popular hobby in Singapore for decades, passed down through generations of fish enthusiasts. Along the way, well-meaning but incorrect advice gets repeated until it becomes accepted wisdom. Some myths are harmless. Others cause real suffering to fish and frustration for their keepers.

Over twenty years at our shop at 5 Everton Park, we have heard every one of these myths from customers who believed them wholeheartedly. This article sets the record straight on fifteen of the most common misconceptions in the hobby.

Myth 1: Fish Grow to the Size of Their Tank

The myth: A fish placed in a small tank will stay small. It will only grow as large as its environment allows.

The truth: Fish do not stop growing to match their tank. What actually happens is that stunted growth occurs — the fish’s body may slow its external growth, but internal organs continue developing, leading to deformities, organ compression and a drastically shortened lifespan. The fish is not “comfortable” in a small tank. It is suffering.

Why it matters: This myth is used to justify keeping large species like oscars, arowanas and common plecos in tanks far too small. Always research the adult size of any fish before purchase and provide an appropriately sized tank.

Myth 2: Goldfish Bowls Are Fine

The myth: Goldfish are hardy fish that thrive in small bowls without filtration.

The truth: Goldfish are among the messiest fish in the hobby. They produce enormous amounts of waste relative to their body size and can grow to 15 to 30 centimetres depending on the variety. A single fancy goldfish needs at minimum a 75-litre tank with strong filtration. Common goldfish belong in ponds, not bowls.

Why it matters: Goldfish in bowls typically die within weeks or months from ammonia poisoning. A properly kept goldfish can live 10 to 15 years or more.

Myth 3: Bettas Like Small Spaces

The myth: Bettas are found in small puddles in the wild, so they prefer tiny tanks.

The truth: Wild bettas live in vast rice paddies, shallow streams and marshes — environments that are shallow but span large areas. They do not choose to live in puddles; they survive in them temporarily during drought. A betta kept in a tiny container is surviving, not thriving. A minimum of 10 litres (ideally 20 to 40 litres) with gentle filtration produces a dramatically healthier, more active and more colourful betta.

Why it matters: Bettas in small unfiltered containers develop fin rot, lethargy and shortened lifespans. Given proper space, they are curious, interactive fish that can live three to five years.

Myth 4: Wait 24 Hours After Adding Conditioner

The myth: After treating tap water with dechlorinator, you must wait 24 hours before it is safe for fish.

The truth: Modern water conditioners like Seachem Prime neutralise chlorine and chloramine within seconds. There is no need to wait. You can treat the water and add it to the tank immediately. This myth likely originates from the old practice of letting water sit out to off-gas chlorine — which does not work for chloramine, the disinfectant used by PUB in Singapore.

Why it matters: Waiting is not harmful, but it is unnecessary and makes water changes more cumbersome. The bigger risk is believing you can skip the conditioner by letting water sit — chloramine does not evaporate.

Myth 5: Algae Means Your Tank Is Dirty

The myth: If you see algae growing, your tank is unclean and poorly maintained.

The truth: Algae is a natural organism present in every body of water on Earth. A small amount of algae in an aquarium is normal and even beneficial — it indicates the tank has a functioning ecosystem. Excessive algae growth usually signals an imbalance in light, nutrients or CO2, not poor cleanliness. Some of the most meticulously maintained tanks in the world have algae outbreaks because the light-nutrient balance was slightly off.

Why it matters: Scrubbing every surface obsessively or using harsh chemical algaecides can harm the tank’s biological balance. The correct approach is to identify and correct the underlying imbalance.

Myth 6: Snails Are Always Bad

The myth: Snails are pests that should be removed on sight.

The truth: Most common aquarium snails (Malaysian trumpet snails, ramshorn snails, bladder snails) are beneficial. They eat decaying plant matter, leftover food and algae. They aerate substrate by burrowing and their population self-regulates based on food availability. An “explosion” of snails usually means you are overfeeding — the snails are a symptom, not the problem.

Why it matters: Many hobbyists spend time and money trying to eradicate snails that are actually helping keep the tank clean. Embrace them as part of the cleanup crew.

Myth 7: More Filtration Means Fewer Water Changes

The myth: If you install a powerful enough filter, you can skip water changes.

The truth: Filters convert ammonia to nitrite to nitrate, but they do not remove nitrate from the water. Only water changes (and to some extent, live plants) remove nitrate. Filters also do not remove dissolved organic compounds, hormones or replenish trace minerals. No amount of filtration replaces regular water changes.

Why it matters: Hobbyists who invest in expensive filtration sometimes neglect water changes, leading to a phenomenon called “old tank syndrome” — slowly rising nitrate and declining water quality that eventually crashes.

Myth 8: Fish Have a Three-Second Memory

The myth: Fish cannot remember anything beyond three seconds, so they do not suffer in poor conditions because they constantly forget.

The truth: Scientific studies have repeatedly demonstrated that fish have long-term memory lasting months. Goldfish can be trained to navigate mazes, respond to sounds and recognise their keepers. Cichlids remember social hierarchies. Fish can learn to associate specific colours with food rewards and retain that knowledge for extended periods.

Why it matters: This myth is used to justify poor care. If fish cannot remember or feel, then small tanks and dirty water do not matter. The science says otherwise.

Myth 9: Aquarium Salt Cures Everything

The myth: Adding aquarium salt is a universal cure for any fish disease.

The truth: Salt is helpful for some conditions — it can reduce nitrite toxicity, treat mild cases of ich and help with osmoregulation in stressed freshwater fish. However, it is harmful to many species (scaleless fish like loaches, most catfish, and invertebrates like shrimp and snails) and ineffective against most bacterial, fungal and parasitic diseases. It is a first-aid tool, not a cure-all.

Why it matters: Using salt instead of appropriate medication delays proper treatment. Sensitive species can be killed by salt concentrations that would help other fish. Always identify the disease first, then treat accordingly.

Myth 10: You Need a Heater in Singapore

The myth: Every tropical aquarium needs a heater, regardless of location.

The truth: Singapore’s ambient temperature stays between 28 and 32 degrees Celsius year-round. This is within the ideal range for virtually all common tropical freshwater fish. A heater is unnecessary in most HDB and condo setups unless the room is air-conditioned to below 24 degrees consistently. In fact, Singapore’s warm temperatures are sometimes too high for temperate species — the concern should be cooling, not heating.

Why it matters: A heater in a room that is already 30 degrees can push water temperature dangerously high if it malfunctions. It is an unnecessary expense and potential risk for most Singaporean fishkeepers.

Myth 11: Bubbles Equal Oxygen

The myth: An air pump producing bubbles adds oxygen to the water. More bubbles means more oxygen.

The truth: The bubbles themselves contribute very little oxygen. Most gas exchange in an aquarium happens at the water surface, where the water meets the air. An air pump helps primarily by creating surface agitation — the rising bubbles disturb the surface, which increases gas exchange. A filter outlet that ripples the surface achieves the same effect without the noise of an air pump.

Why it matters: Hobbyists sometimes rely solely on an air stone while neglecting surface agitation from the filter. Conversely, planted tank keepers who want to retain CO2 should know that surface agitation (not just bubbles) is what drives CO2 off-gassing.

Myth 12: Gravel Is Better Than Sand

The myth: Gravel is the superior substrate because sand compacts, traps gas and kills fish.

The truth: Both substrates have pros and cons. Sand compacts more than gravel, but Malaysian trumpet snails (common in Singapore) aerate sand naturally. Sand is better for bottom-dwelling fish like corydoras, whose delicate barbels can be damaged by sharp gravel. Anaerobic pockets in sand are rarely dangerous in a well-maintained tank with adequate flow. Many professional aquascapers prefer fine sand or aquasoil over gravel.

Why it matters: This myth discourages beginners from using sand, which is often the better choice for planted tanks and bottom-dwelling species.

Myth 13: Leave Lights on 12+ Hours for Plants

The myth: Aquatic plants need as much light as possible. Leave the light on 12 or more hours a day for maximum growth.

The truth: Most aquatic plants do well with six to eight hours of light per day. Exceeding this, especially without adequate CO2 and fertilisation, fuels algae growth rather than plant growth. Plants can only photosynthesise up to a point determined by available CO2 and nutrients. Light beyond that point benefits only algae, which are less limited by CO2.

Why it matters: Excessive lighting is the single most common cause of algae outbreaks in planted tanks. Use a timer and limit the photoperiod to six to eight hours.

Myth 14: Bigger Fish Always Eat Smaller Fish

The myth: Any fish large enough to fit another fish in its mouth will eat it.

The truth: While many predatory species will eat smaller tank mates, plenty of large fish are peaceful herbivores or micro-feeders that ignore smaller companions. Bristlenose plecos, otocinclus, large peaceful rasboras and many catfish species coexist happily with small fish. Temperament varies by species, not solely by mouth size. That said, it is wise to avoid combining obviously predatory species with bite-sized tank mates.

Why it matters: This myth limits stocking choices unnecessarily. Research individual species’ temperaments rather than relying on size alone.

Myth 15: You Cannot Overfilter a Tank

The myth: There is no such thing as too much filtration. More is always better.

The truth: While having filtration capacity above your tank’s minimum requirement is generally good, excessively powerful filters create problems. Strong currents stress slow-moving fish like bettas, long-finned guppies and many dwarf shrimp. Powerful flow can uproot plants, redistribute substrate and make it difficult for fish to feed. In planted tanks, excessive surface agitation drives off CO2 that plants need.

Why it matters: Matching filter flow rate to the inhabitants’ needs is important. A canister filter rated for 400 litres on a 30-litre betta tank creates a washing-machine environment that harms the fish.

Frequently Asked Questions

Where do these aquarium myths come from?

Most originate from outdated practices, pet-shop sales tactics or misunderstandings passed between hobbyists. The hobby has evolved significantly over the past twenty years, but old advice lingers in online forums, social media groups and well-meaning conversations at fish shops. Always cross-reference advice with current, evidence-based sources.

Are there any myths specific to fishkeeping in Singapore?

The heater myth (number 10) is particularly relevant. Many global care guides insist on heaters because they are written for temperate climates. In Singapore, a heater is usually unnecessary and can even be counterproductive. Additionally, the assumption that PUB tap water can be left to stand to remove chlorine is dangerous — Singapore uses chloramine, which does not evaporate and must be neutralised chemically.

How can I tell if advice I receive is a myth or fact?

Look for advice backed by biology rather than anecdote. If someone says “I have always done it this way and my fish are fine,” that is anecdotal. If the advice can be traced to peer-reviewed research, veterinary guidance or established aquarium-science principles, it is more likely to be reliable. When in doubt, consult a trusted aquascaping professional.

Have Questions About Your Setup?

Misinformation costs fishkeepers time, money and — most importantly — the health of their fish. If you have heard advice that sounds suspect, or if you want to fact-check something before acting on it, visit us at 5 Everton Park. With over twenty years in the hobby, we have the experience to separate fact from fiction and help you make decisions based on evidence, not myth.

Get in touch or drop by the shop — we are always happy to set the record straight.

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