Goldfish are native to temperate waters of East Asia where they have lived for millions of years, surviving both drying-out summers as well as freezing winters in their ponds. Seeing goldfish kept in bowls with heaters has led some to believe it’s necessary to heat the water. Even though goldfish were never meant to live in heated water.
Heating the water is most often a well-intentioned error by hobbyist, fueled by a fear of cold water equating to dead fish. For the right species, the reality is far kinder. Yes, goldfish aren’t tropical fish, nor do it require water to be constantly at seventy-eight degrees all year long.
Seventy-eight can stress them out and shorten their life span. The problem isn’t so much providing the heat as it is coping with its absence. And you have to get your head around what happens biologically when the water falls below sixty.
Essential Tips for Unheated Goldfish Care
Choosing Hardy Goldfish Varieties
First things first… Pick your fish wisely. Not all goldfish fare well in the cold.
Delicate-finned fancy goldfish (balloon bodied types) does not like the cold. Both their swim bladder and their compressed internal organs is unpredictable. If you get a Ryukin or a Ranchu, it probably won’t make it in your unheated tank.
Instead, select a streamlined swimmer that’s also hearty. In the cold-water world, there is two workhorse goldfish: the Comet goldfish and the Common goldfish. These fish has a deep body which adapts to temperature changes easy.
Adjusting Feeding in Cold Water
This is basic biology for long-term health. As the season progresses, the feeding routine need to change drasticly too. Don’t feed what you did in July in January.
As the water gets colder, a goldfish’s metabolism slow down a lot. Below 50 degrees they hardly eat at all and completely shut off below 40 degrees. Food left sitting in the tank will go bad.
Bad food raises ammonia. Ammonia is toxic, including on cold water. Stop feeding (or severely restrict) during deep winter.
Just a light dusting once weekly are enough. The fish have plenty of stored fat that will get them through. New owners has trouble believing this, but again it’s critical to water quality.
Maintaining Stable Tank Temperature
Where the tank sits will dictate what temperature range it might sit in. In practice, there’s no such thing as an unheated room. Even if house isn’t heated, your garage or basement won’t be hot.
It also won’t fluctuate much. Your sunroom on the other hand might swing like crazy. Stability is good for goldfish; shock is not.
A 10 degree drop overnight is worse than a constant 40 degree tank temp. Avoiding any type of thermal shock are important. Keeping the tank out of direct sunlight and direct drafts help create that consistency.
That’s where consistency save more fish than warmth does. In a cold environment, filtration has to be thought about different. Cold water inhibits growth rate of beneficial bacteria.
Winter Filtration and Water Quality
Your filter is still up and running, but only operating at a fraction of its summer capacity. Clean your filter media in winter, if necessary, by rinsing gently in tank water (not tap water). You’ll kill the slow growing bacteria if you use tap water.
A healthy biological filter are your best friend when trying to prevent ammonia spikes. As metabolism decreases, so does waste production. However, the bacteria is reproducing less as well.
Again, balance is key. Don’t mess around too much with the filter, let it do its job. Goldfish keeping is as much (or perhaps even more) an exercise in patience then it is heat.
Understanding Dormant Behavior
They’ll become less active, sluggish, and even a bit colorless. It’s nothing to worry about; they’re going into a sort of semi-dormant stage. Sometimes you won’t see them for days except maybe hanging around the tank bottom.
Don’t feed them more. Don’t throw more light at them, and above all, do not panic! Let them be.
Let them go through their natural cycle. The unheated-tank goldfish who survive best are those whose keepers believes in the process. Reduce feeding, maintain a stable tank environment, and let the fish do what they need to do…and then give you a show when the warmer weather rolls back around.
Going back to the roots of keeping goldfish; without a heater, makes sense. Respecting their biology, it also keeps things simple. Instead of a constant humming heater, you get to appreciate the changing seasons.
Give ’em some time off and room to breathe; they’ll be okay. In the end, the tank will become a livig indicator of what’s happening outside. That’s worth waiting for.
