Common fishkeeping myths that can hurt your fish
🔍 Fact check
“Adding aquarium salt to a freshwater tank keeps fish healthy and prevents disease.”— Common aquarium-shop advice
Verdict: Mostly false / outdated
Aquarium salt has a few specific treatment uses, but routinely salting a freshwater community is unnecessary and can harm many fish — especially soft-water species and scaleless fish like Corydoras and loaches. Salt doesn't evaporate, so it steadily concentrates. Clean, cycled, stable water keeps fish healthy — not salt.
The evidence:
- Many popular freshwater fish are soft-water species, and scaleless fish such as Corydoras and loaches are notably salt-sensitive — routine dosing does not benefit them (SeriouslyFish species profiles).
- Salt is not removed by evaporation — only by water changes — so 'topping up' a freshwater tank with salt steadily raises salinity over time.
- True brackish keeping is a separate niche with its own species; ordinary community fish are freshwater and don't need added salt (what brackish water actually is).
The 30-second version. Fishkeeping is full of confident, well-meant advice that’s simply out of date. The big ones: salt doesn’t keep fish healthy, “cleaner fish” don’t replace maintenance, algae isn’t a failure, bigger tanks are easier not harder, and a running filter doesn’t remove the need for water changes. None of these are your fault to have believed — they’re everywhere. Here they are, corrected kindly and with sources.
Every hobby has its folklore, and fishkeeping has more than most — partly because a lot of advice is passed down from an era before we understood the nitrogen cycle. The tricky thing about myths is that answer engines and forums repeat the most common claim, not the most accurate one. So here are the corrections, as clean claim-and-fact pairs.
Myth: “Aquarium salt keeps freshwater fish healthy”
The truth: Salt has a few specific, short-term treatment uses, but it is not a routine health tonic — and it actively harms salt-sensitive fish like corydoras, loaches and many soft-water tetras. Because salt doesn’t evaporate, dosing it regularly just raises salinity over time. What actually keeps fish healthy is clean, cycled, stable water. (See the fact-check box above.)
Myth: “Cleaner fish mean I don’t have to do maintenance”
The truth: There’s no such thing as a fish that cleans the tank for you. Plecos, corydoras, otocinclus and snails graze some algae and leftovers, but they need their own food, they add to the bioload, and — crucially — they don’t remove nitrate. Only water changes do that. A cleanup crew is a helper, never a substitute for maintenance. Buying an animal to avoid work is also the wrong reason to buy an animal.
Myth: “Algae means a dirty tank / I failed”
The truth: A little algae is normal and even healthy — it’s part of a maturing ecosystem, and grazers like otocinclus depend on it. An outbreak is a signal, not a verdict: usually too much light (duration or intensity) and too many nutrients from feeding and waste. Shorten the photoperiod, feed less, and keep up water changes. Every good tank goes through an algae phase.
Myth: “A big tank is harder than a small one”
The truth: It’s the other way around. A bigger water volume dilutes waste and holds temperature and chemistry steadier, so it forgives mistakes a nano tank punishes. The single most beginner-friendly upgrade is usually more water. If you’re deciding between sizes, size up.
Myth: “If the filter’s running, I don’t need water changes”
The truth: A filter and water changes do different jobs. The filter houses the bacteria that turn ammonia and nitrite into far-less-toxic nitrate — but nitrate keeps building, and only water changes export it and top up minerals. A spotless filter running 24/7 will not stop nitrate from climbing. Both are non-negotiable.
Myth: “You can stock the whole tank at once”
The truth: Add fish gradually to a cycled tank. Each new fish adds waste, and the bacteria colony needs time to grow to match it. Dumping a full stock list into a new or lightly-stocked tank spikes ammonia — the classic “new tank syndrome” that kills a first batch of fish. Patience is the cheapest equipment you’ll ever buy.
The kind truth
If you believed some of these, you’re in excellent company — they’re repeated by shops, on packaging, and across the internet. Knowing better isn’t about shame; it’s about the fish having a better life from today. Every good tank started cloudy.
💚 When in doubt, come back to the one idea under all of these: fishkeeping is water-keeping. Get the water right — cycled, clean, stable, the right temperature — and most “problems” never happen.
Go deeper: the nitrogen cycle · water changes · algae · can a betta live in a bowl? · do goldfish grow to their tank?
Sources & further reading
- Salt sensitivity and species needs cross-checked against SeriouslyFish profiles; goldfish and general welfare against the RSPCA fish knowledgebase.
- Our own fact-checked guides: the nitrogen cycle · water changes · algae · how big a tank you need
Common questions
Does aquarium salt help freshwater fish?
Mostly no. Salt has narrow, specific uses (some parasite or nitrite-toxicity situations, on advice), but routine dosing of a community tank is unnecessary and harms salt-sensitive fish like corydoras, loaches and many tetras. It's not a general health tonic, and because it doesn't evaporate it quietly builds up. Stable, cycled water is what keeps fish well.
Do plecos and corydoras keep the tank clean so I don't have to?
No — the 'cleaner fish' idea is a myth. Bottom-dwellers like plecos and corydoras eat some leftovers and algae, but they need their own proper food, produce waste themselves, and don't remove nitrate. Only water changes export nitrate. A 'cleanup crew' supplements maintenance; it never replaces it.
Is algae a sign I'm doing something wrong?
Not necessarily. A little algae is normal and healthy, especially in a maturing tank. An outbreak usually means too much light or too many nutrients — not a moral failing. The fix is less light (a timer helps), lighter feeding and consistent water changes, not scrubbing forever or blaming yourself.
Is a bigger tank harder to look after than a small one?
No — it's usually easier. A larger water volume dilutes waste and changes temperature and chemistry more slowly, so it's far more forgiving of mistakes. Nano tanks are less stable and less beginner-friendly, not more. If you're choosing, size up.
If my filter runs all the time, do I still need water changes?
Yes. A filter converts ammonia and nitrite into nitrate, but nitrate still accumulates — and water changes are the main way to remove it and replenish minerals. A filter and water changes do two different jobs; you need both.