Fish · Cyprinus carpio · typical adult weight 0.25–20.00 kg
Formalin (37% formaldehyde solution) is dosed at 25–50 mg/L of water (immersion) Immersion (bath) Single treatment; repeat if organic load high in koi, per Hadfield CA, Clayton LA, eds. Clinical Guide to Fish Medicine. 1st ed. Hoboken, NJ: Wiley-Blackwell; 2021. p.507. Formalin (37% formaldehyde solution) is used in koi for Trichodinids (Trichodina, Trichodinella, Paratrichodina, Tripartiella spp.), Gyrodactylid monogeneans (skin and gill flukes) - high-dose protocol, Ichthyophthirius multifiliis (freshwater ich / white spot). Routes documented in koi: Immersion (bath). A typical adult koi weighs 0.25–20.00 kg. ExoticRx lists 3 cited dose rules for Formalin (37% formaldehyde solution) in koi, drawn from published veterinary references. Verify against current literature before clinical use.
US trade names: Formalin-F, Formacide-B, Parasite-S
| Route | Dose | Frequency | Duration | Indication | Evidence | Source |
|---|---|---|---|---|---|---|
| Immersion (bath) | 25–50 mg/L of water (immersion) | Single treatment; repeat if organic load high | Contact time 1-2 hours. "A single treatment is often enough unless organic load remains high." | Trichodinids (Trichodina, Trichodinella, Paratrichodina, Tripartiella spp.) | Moderate | Hadfield CA, Clayton LA, eds. Clinical Guide to Fish Medicine. 1st ed. Hoboken, NJ: Wiley-Blackwell; 2021. p.507.Compilation only — we have not located an independent source that prints this figure. |
| Immersion (bath) | 250 mg/L of water (immersion) | Every 7 days for 3 treatments | Contact time one hour per treatment, every seven days, for a course of three. | Gyrodactylid monogeneans (skin and gill flukes) - high-dose protocol | Weak | Hadfield CA, Clayton LA, eds. Clinical Guide to Fish Medicine. 1st ed. Hoboken, NJ: Wiley-Blackwell; 2021. p.534.Compilation only — we have not located an independent source that prints this figure. |
| Immersion (bath) | 40–100 mg/L of water (immersion) | q48h at 9-11C or q24h at 17-20C; 5-7 treatments | Contact time 1-2 hours per treatment. Course is TEMPERATURE-dependent as printed: five to seven treatments every 48 hours at 9-11 C (48-52 F) and every 24 hours at 17-20 C (63-68 F); at higher temperatures the dosing frequency may need to be at least twice daily. | Ichthyophthirius multifiliis (freshwater ich / white spot) | Moderate | Hadfield CA, Clayton LA, eds. Clinical Guide to Fish Medicine. 1st ed. Hoboken, NJ: Wiley-Blackwell; 2021. p.494.Compilation only — we have not located an independent source that prints this figure. |
Every held source for this drug and species, as printed. Where they differ, both are shown — the choice is yours, not ours.
| Dose (%) | Route | Source | As printed |
|---|---|---|---|
| 30 | IMMERSION | Carpenter's Exotic Animal Formulary, 6th edTable 2.1 | - 0.23 mL/L bath × up to 60 min 1 mL/3.8 L bath × 12-24 hr followed by 30%-70% water change, may be repeated 1-2 mL/L bath × up to 15 min |
| 70 | IMMERSION | Carpenter's Exotic Animal Formulary, 6th edTable 2.1 | - 0.23 mL/L bath × up to 60 min 1 mL/3.8 L bath × 12-24 hr followed by 30%-70% water change, may be repeated 1-2 mL/L bath × up to 15 min |
| Dose (ppm) | Route | Source | As printed |
|---|---|---|---|
| 200 | IMMERSION | Carpenter's Exotic Animal Formulary, 6th edTable 2.2 | 200 ppm bath × 1 hr |
Typical range: 0.25–20 kg
If provided, volume will be calculated alongside dose.
Reference only. Verify against current literature before clinical use.
IMMERSION USE ONLY in fish - formalin is added to the water, never injected or given orally. It strips dissolved oxygen from the water, so supplemental aeration is mandatory and dissolved oxygen and biological filtration must be monitored throughout treatment. Toxicity rises as temperature rises and as oxygen falls. Some fish and invertebrate species and some life stages are formalin-sensitive; scaleless fish, fry and heavily parasitised fish are least tolerant. High-dose protocols (250 mg/L) are documented as capable of causing morbidity and mortality. Formalin is a human carcinogen - suitable PPE is required when handling it. Discard any formalin containing visible white paraformaldehyde precipitate: it is far more toxic to fish than the clear solution.
Species-specific contraindications and adverse-reaction reports for koi may differ from canine / feline reference data — consult the primary citations listed with each rule.
Formalin (37% formaldehyde solution) dose ranges in koi, with cited source references: Immersion (bath) 25–50 mg/L of water (immersion) Single treatment; repeat if organic load high; Immersion (bath) 250 mg/L of water (immersion) Every 7 days for 3 treatments; Immersion (bath) 40–100 mg/L of water (immersion) q48h at 9-11C or q24h at 17-20C; 5-7 treatments. Reference ranges from cited sources — verify against current literature before clinical use.
Documented routes for Formalin (37% formaldehyde solution) in koi: Immersion (bath).
Cited course lengths for Formalin (37% formaldehyde solution) in koi include: Contact time 1-2 hours. "A single treatment is often enough unless organic load remains high."; Contact time one hour per treatment, every seven days, for a course of three.; Contact time 1-2 hours per treatment. Course is TEMPERATURE-dependent as printed: five to seven treatments every 48 hours at 9-11 C (48-52 F) and every 24 hours at 17-20 C (63-68 F); at higher temperatures the dosing frequency may need to be at least twice daily.. Duration depends on the indication — match it to the specific dose rule in the table above.
Formalin (37% formaldehyde solution) is indicated in koi for: Trichodinids (Trichodina, Trichodinella, Paratrichodina, Tripartiella spp.), Gyrodactylid monogeneans (skin and gill flukes) - high-dose protocol, Ichthyophthirius multifiliis (freshwater ich / white spot).
These are general warnings for Formalin (37% formaldehyde solution) across species; consult the koi dosing table above for species-specific guidance. IMMERSION USE ONLY in fish - formalin is added to the water, never injected or given orally. It strips dissolved oxygen from the water, so supplemental aeration is mandatory and dissolved oxygen and biological filtration must be monitored throughout treatment. Toxicity rises as temperature rises and as oxygen falls. Some fish and invertebrate species and some life stages are formalin-sensitive; scaleless fish, fry and heavily parasitised fish are least tolerant. High-dose protocols (250 mg/L) are documented as capable of causing morbidity and mortality. Formalin is a human carcinogen - suitable PPE is required when handling it. Discard any formalin containing visible white paraformaldehyde precipitate: it is far more toxic to fish than the clear solution.
Why a species-specific page? Formalin (37% formaldehyde solution) pharmacokinetics differ across species: dose ranges, intervals, and route preferences are not interchangeable. Cross-extrapolation from canine doses is unsafe in koi — the rules above are the citations specific to this species, not generic recommendations.
Sourced from published veterinary references; awaiting credentialed clinical reviewer. See our editorial process. Reference only — not veterinary advice.
| 250–400 | IMMERSION | Carpenter's Exotic Animal Formulary, 6th edTable 2.2 | 250-400 ppm bath × 1 hr followed by 5 min freshwater dip |
| 400 | IMMERSION | Carpenter's Exotic Animal Formulary, 6th edTable 2.2 | 0.4 mL/L (400 ppm) bath × up to 1 hr q3d × up to 3 treatments |
| 500 | IMMERSION | Carpenter's Exotic Animal Formulary, 6th edTable 2.2 | 0.5 mL/L (500 ppm) bath × up to 1 hr q3d × up to 3 treatments |
Figures are transcribed from the cited page or table of each held edition and are shown for reference only. They are not dose recommendations, they do not feed the calculator, and none has been reviewed by a veterinarian.