Goldfish are the hamsters of the water world. Three good reasons they’re usually shorter-lived than political promises:
a) bought from places that don’t follow ideal/scrupulous quarantine/hygiene procedures
b) transported home AND/OR housed in too-small containers lacking good oxygenation, lacking a proper buffer against rapid temperature fluctuations, and poor filtering/water recycling. (a goldfish bowl with no bubbler and no filtering is a gold-plated invitation for disease)
c) bought by people who don’t follow proper protocol for new fish introductions, and think goldfish are naturally sturdy animals that can live in “cold water” (they’re ancestors were tougher, but hybridization tends to reduce vigor and tolerance to extremes)
I concur with Sophie that fungal disease is a major cause of aquarium mortality, although salt therapy is controversial since species vary in their tolerance to salt. As a prophylactic (adding tiny amounts to the community tank), it usually works well, and prevention is far easier than identifying and curing. With small cheap goldfish, it’s rarely worth the effort or cost to attempt antibiotic “cures” and positive ID of the disease needs to be immediate and accurate, else the cure might be worse than the disease.
Segregation in a separate “hospital” tank with a different water source (no chained filtration systems) is important with many problems. Antibiotic use by fish enthusiasts is, imho, as bad as their use in everyday life. A “treated” tank’s entire balance is often thrown out of whack as anti-b’s, esp. broad spectrum varieties, typically kill off both good and bad microbes. I’ve never had a community tank truly recover its natural balance after dosing with anti-b’s, another reason isolation tanks are a good idea.
Many pathogens, incl. ICH, exist in pretty much all aquaria. Fish vigor is what hinders pathogen populations from gaining a foothold, erupting and spreading. Using a vague term - “white spots” - makes it impossible to diagnose a problem sight unseen. Always try to differentiate between something like Ichthyophthirius (known as “ICH”) and various other problems -
http://badmanstropicalfish.com/fish_p…
Temperature “shock” reduces both vigor, likely affecting the protective slime fish exude, allowing pathogens to find chinks in the slime “armor”. Treatment with a mild malachite green product works well, provided you catch the disease early and maintain the treatment for AT LEAST a 12-day period, preferably followed by a half-treatment for a few more days or until no more spots can be seen on any fish.
“Cold water” is a misnomer, and total water exchanges aren’t ideal even though goldfish produce a LOT of polluting debris. Frequent partial water changes are best. Water temp is one of the most crucial factors in maintaining indoor goldfish vigor. They do best in temps in the low 60’s (which isn’t your typical house temp, btw). In winter, tap water often flows below that. Once temps dip below about 54°, goldfish stop eating (or metabolizing) food. That’s why acclimatization is important, during both initial fish introductions and during cleanings, and why a larger aquarium than the typical under-1-gallon size goldfish “bowl” provides some insulating buffer against nighttime air temp fluctuations.
Designate a large container for storage, keep it filled with water that has time to reach room temp and outgas the chlorine additives. Use that water to replace water vacuumed from the bottom of a tank, then refill the storage container with colder tap water and let it climb to room temp and outgas until the next cleaning.
Any informative goldfish web page guide should contain roughly the same info, i.e., -
http://www.wikihow.com/Make-a-Goldfis…
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