Keeping Goldfish Properly

Introduction

Goldfish are among the most misunderstood fish in the hobby. Sold as easy starter pets and often kept in tiny bowls, they are actually messy, long-lived fish that can grow surprisingly large and live for 10–20 years with proper care. Getting goldfish care right is genuinely rewarding, but it requires debunking some very common myths first.

Quick Overview

Types of Goldfish

Single-Tailed Goldfish

Common goldfish, comets, and shubunkins have slim, torpedo-shaped bodies and a single tail fin. They are hardy, fast swimmers, and can grow 12 inches or more. These fish are best suited to ponds or very large tanks (75+ gallons for a few fish).

Fancy Goldfish

Orandas, ryukins, ranchus, and telescope-eyed varieties have round, double-tailed bodies and grow to 6–8 inches. They are slower swimmers and more delicate. A 40-gallon tank is a reasonable starting point for one or two fancy goldfish, with 10 extra gallons per additional fish.

Tank Size and Filtration

Goldfish are exceptionally messy. They eat constantly and produce large amounts of waste, meaning ammonia builds up fast. A filter rated for 2–3 times your tank volume per hour is a good starting point. Many goldfish keepers run canister filters or sump setups for extra capacity.

Goldfish also benefit from surface agitation for oxygenation. Adding an airstone or choosing a filter with a spray bar output helps keep dissolved oxygen levels high, especially important since goldfish are cold-water fish and cold water holds more oxygen than warm water.

Water Parameters

Goldfish are cold-water fish and do not need a heater in most homes. Their ideal temperature range is 65–72F, though they can tolerate 50–75F. Keeping them too warm reduces dissolved oxygen and stresses them over time.

• Temperature: 65–72F (no heater needed in most homes)
• pH: 7.0–8.0
• Ammonia: 0 ppm
• Nitrite: 0 ppm
• Nitrate: below 20 ppm with regular water changes

Feeding Goldfish

Goldfish are omnivores and will eat almost anything. Feed a high-quality sinking pellet as a staple, which reduces the amount of air goldfish gulp when eating from the surface (a contributor to swim bladder issues in fancy varieties). Supplement with:

• Blanched vegetables: peas, spinach, zucchini, cucumber
• Occasional protein treats: brine shrimp, daphnia, bloodworms

Feed small amounts once or twice a day. Goldfish have no stomach, so overfeeding leads to rapid water quality decline. A good rule: feed only what they can consume in 2–3 minutes, then remove any uneaten food.

Common Health Issues

Many goldfish health problems trace back to poor water quality. The most common issues include:

• Swim bladder disorder: Fish float sideways or sink. Often caused by constipation or gulping air. Try fasting for 2–3 days, then offering blanched peas.
• Ich: White spots resembling salt grains. Treat with ich medication and raise temperature slightly (to 74F).
• Fin rot: Ragged, discolored fins. Improve water quality first; mild cases often resolve with clean water alone.
• Anchor worms and flukes: External parasites more common in pond goldfish or fish from outdoor sources. Treat with appropriate antiparasitic medications.

Tank Mates

Goldfish do best with other goldfish of similar size and body type. Avoid mixing single-tailed and fancy varieties, as single-tailed goldfish are faster and will outcompete fancies for food. Suitable companions for fancy goldfish include white cloud mountain minnows and certain snails and plecos, though plecos may occasionally suck on goldfish slime coats.

Avoid tropical fish entirely. The temperature mismatch means one group will always be kept outside its ideal range.