and id have to disagree with the heater and 5 gallon. its better for them, but ive had bettas live in goldfish bowl w/o a heater, and live for 5 yrs+
For starters goldfish are cold water creatures while your average fighting fish is planted firmly in the tropical fish family. So while goldfish love to frolic in the cold, bettas prefer the warmer waters. For this reason goldfish need to be housed in an environment with a temp of 50-60 degrees Fahrenheit while bettas prefer living with a heater keeping the water at 76-82 degrees.
A bigger reason why bettas can't live with goldfish is because the latter are quite notorious for producing prodigious amounts of toxic waste. And if you carefully did your research on betta fish care, you should know that these finny divas have a low tolerance for waste and toxins in their water. So while goldfish don't mind swimming through their own poop bettas would. In fact, they tend to die off if they are exposed to even slight amounts of ammonia and nitrates in the water.
Can You Put Goldfish With A Betta Fish? | My Aquarium Club
Can Betta Fish Live With Goldfish? | betta fish care articles
Myth: Bettas can be kept with goldfish since both live happily in bowls. Reality: This myth is multi-dimensional. Bettas are arguably unsuitable for keeping in bowls due to the difficulties in maintaining appropriate temperature. Goldfish should never be kept in bowls due to their waste output, oxygenation needs, and growth potential. Improper housing aside, the two species are incompatible. Bettas are small, solitary, aggressive tropical fish which require soft, acidic, still water and pristine conditions. Goldfish are large, social, fin-nipping coldwater fish which demand harder, slightly base, well-oxygenated and filtered water. They are also massive waste producers and hosts to many parasites. In short, the two species are utterly incompatible, and should not be housed together under any circumstances - especially in bowls! I don't think bettas would attack just any red fish--I put bettas with reddish neons and marble goldfish that had red in them and they didn't attack. Or would they only attack red fish that had big fins and acted aggressive?That aside, I agree with all of the above posters; you can not keep bettas and goldfish together. Goldfish need a large tank with a powerful filter and aerator since they are cold water fish, and grow to a size where the betta would eventually be more at risk than the goldfish. Bettas, while they thrive in larger aquariums as long as there are plenty of plants to hide among, prefer still to low-current water and do best on the warmer end of the tropical range.If you are trying to choose between a Goldfish or Betta, for the purposes of this article let’s assume you are interested in keeping your fish in the healthiest way possible. I hope that’s true, but, sadly, not everyone cares about the well-being of a lowly fish, and they end up in poor conditions with failing health and shortened lives.