Disclaimer: Hobbyist reference — not veterinary diagnosis. This is a shopping list; doses live on Medications. Verify doses on current labels. Full text: About / Disclaimer.
Goldfish starter kit
What to have on the shelf before something goes wrong. Buying it after, at 9 p.m. on a Sunday, is less fun.
- Two buckets. One for dirty water, one for clean. They're fish buckets now. Not for mopping, not for the car.
- A siphon of some sort. Gravel vac, length of hose, whatever gets water from the tank to the dirty bucket.
- Dr. Erik Johnson's book, Koi Health & Disease: Everything You Need To Know (2nd ed.). Says koi on the cover; works for goldfish.
- Water conditioner. Takes the chlorine/chloramine out of tap water. Well water may not need it.
- Salt. Aquarium, pickling, ice cream or water-softener salt are all fine — NaCl is NaCl. Get plain salt with no additives, and weigh it on a kitchen scale. How much and when: Salt (NaCl).
- A small kitchen scale. Mostly for salt: it doses by weight, so weigh, don't scoop. Big tanks and ponds take a lot of it — 0.3% in 100 US gallons is about 1.14 kg (3 g/L × 378.5 L) — so get a scale with enough capacity, or weigh in batches. Optional: a 0.01 g jewelry scale for small med amounts like praziquantel powder.
- A quality pellet food. Sinking or soaked works best; dry floating pellets can mean gulped air and a fish that floats.
- Test kit, drops or strips. We're checking whether a chemical is there so we can make decisions, not making meth. Ammonia, nitrite, nitrate and pH; GH/KH if you can. What each one tells you: What to test for and why.
What to test for and why
| Test | What it tells you |
|---|---|
| Ammonia (NH₃/NH₄⁺) | Toxic. Usually means the tank isn't cycled, or it's overloaded. If ammonia or nitrite > 0: large change with matched water (Sick fish guide). Ammonia is more toxic at high pH (Diseases). |
| Nitrite (NO₂⁻) | Toxic. Also an uncycled tank. Same rule as ammonia: above zero, change water. |
| Nitrate (NO₃⁻) | Not toxic the way the first two are, but high levels mean you should be doing more water changes. |
| pH | How acidic or alkaline the water is. |
| GH | General hardness: dissolved calcium and magnesium. |
| KH | Carbonate hardness: the buffer. |
What we really care about is the water's ability to resist pH swings, and that's mostly KH. Low pH can make a tank take longer to cycle. Goldfish prefer the higher, alkaline end, not acidic.
Quarantine without a cycled filter
One way to quarantine new fish without a cycled filter:
- Double the dose of water conditioner, and add 0.15% salt (1.5 g per liter ≈ 5.7 g per US gallon, weighed). Salt details: Salt (NaCl).
- Why it works: the conditioner binds up the ammonia (only if it's an ammonia-binding conditioner — check the label for that claim), and the salt, specifically the chloride, protects the fish from nitrite.
- Weekly water changes. Redose conditioner and salt for just the volume of water you replaced, not the whole tank. That keeps the chemical safety net working.
- Keep testing ammonia and nitrite during quarantine (what to test for and why).
Why not just use a pre-cycled filter? You can. It's a trade-off: safer for water chemistry, but it's a disease vector for the new fish. Your existing fish can be carrying parasites without showing symptoms.
- Medicine chest, if you want something beyond salt:
- Praziquantel
- Metronidazole
- Kanamycin
- Methylene blue
- Formalin + malachite green (e.g. Rid-Ich Plus by Kordon)
Brands change, get renamed and get reformulated. Check the active ingredient on the label, not the name on the front.