Koi Treatment Dose Calculator: Medication by Pond Volume
Potassium permanganate has a lethal dose that's only 2–3× the therapeutic dose. Formalin at treatment concentrations removes up to 90% of dissolved oxygen from the water. Getting these calculations right isn't a matter of precision for its own sake - it's the difference between a treatment that works and a treatment that kills your fish.
This page covers dose calculations for the core koi treatment chemicals, with worked examples for typical tank and pond volumes.
TL;DR
- Formalin at treatment concentrations removes up to 90% of dissolved oxygen from the water.
- 10–20 mg/L for short dip baths (20–30 minutes maximum, continuous observation).
- If the water stays brown within 30 minutes, the organic load has consumed the PP and the dose needs to be higher to maintain therapeutic concentration.
- At 25 mg/L in warm water (above 68°F/20°C), oxygen depletion can be severe.
- Reduce dose by 25–50% at water temperatures above 70°F.
- A 37% formalin solution contains 370 mg/mL of formaldehyde (approximately - commercial formaldehyde solutions are not always exactly 37%).
- Select the treatment (KMnO4, formalin, praziquantel, salt, or custom) 2.
Potassium Permanganate (KMnO4)
Therapeutic range: 2–4 mg/L for pond treatment. 10–20 mg/L for short dip baths (20–30 minutes maximum, continuous observation).
What it treats: External parasites (flukes, Costia, Trichodina), bacterial surface infections, Columnaris.
The organic load complication: Organic material (dissolved organics, fish waste, algae) consumes potassium permanganate through oxidation - meaning more organic load requires higher doses to maintain effective concentration. This is why PP dosing in a heavily loaded pond differs from a clean koi quarantine program tank.
Color as a guide: In clear, clean water, 2 mg/L PP appears light pink/red. If the water stays brown within 30 minutes, the organic load has consumed the PP and the dose needs to be higher to maintain therapeutic concentration.
Calculation
Target: 2 mg/L
Volume: 3,000 gallons = 11,355 liters
KMnO4 needed: 2 mg/L × 11,355 liters = 22,710 mg = 22.7 grams
For 4 mg/L in the same pond: 45.4 grams
Practical note: Potassium permanganate is a strong oxidizer and a purple-black crystalline solid. Pre-dissolve in a bucket of pond water before adding. Do not touch with bare hands. Wear gloves and eye protection.
Neutralizer: Hydrogen peroxide (3%) neutralizes PP immediately - have 500 mL accessible during any PP treatment for emergency termination if fish show severe distress.
Typical Doses by Volume
| Volume | 2 mg/L | 4 mg/L |
|--------|--------|--------|
| 200 gal (757 L) | 1.5g | 3.0g |
| 500 gal (1,893 L) | 3.8g | 7.6g |
| 1,000 gal (3,785 L) | 7.6g | 15.2g |
| 3,000 gal (11,356 L) | 22.7g | 45.4g |
| 5,000 gal (18,927 L) | 37.9g | 75.7g |
Formalin (37% Formaldehyde Solution)
Therapeutic range: 15–25 mg/L (15–25 mL of 37% solution per 1,000 liters) for prolonged bath treatment.
What it treats: Monogenean flukes, protozoan parasites, Saprolegnia. One of the most effective broad parasite treatments available.
The oxygen problem: Formalin chemically consumes dissolved oxygen. At 25 mg/L in warm water (above 68°F/20°C), oxygen depletion can be severe. Always run maximum aeration. Reduce dose by 25–50% at water temperatures above 70°F.
Calculation
The active ingredient is formaldehyde. A 37% formalin solution contains 370 mg/mL of formaldehyde (approximately - commercial formaldehyde solutions are not always exactly 37%).
To achieve 15 mg/L of formalin (not formaldehyde) in a 500-gallon (1,893 L) tank:
15 mg/L × 1,893 L = 28,395 mg = 28.4 mL of 37% formalin solution
To achieve 25 mg/L in the same tank:
25 mg/L × 1,893 L = 47,325 mg = 47.3 mL of formalin
Temperature Safety Adjustments
| Water Temperature | Maximum Formalin Dose |
|------------------|----------------------|
| Below 65°F (18°C) | 25 mg/L standard |
| 65–70°F (18–21°C) | 20 mg/L |
| 70–75°F (21–24°C) | 15 mg/L |
| Above 75°F (24°C+) | Avoid or use only with intensive monitoring at ≤10 mg/L |
Do not use formalin at temperatures above 80°F (27°C) unless you have continuous DO monitoring and emergency water change capability immediately available.
Praziquantel
Therapeutic range: 2–5 mg/L in the water column. Higher end of range for heavy infestations.
What it treats: Monogenean flukes - Dactylogyrus (gill flukes) and Gyrodactylus (skin flukes). Also effective against tapeworms in food.
Safety profile: One of the safer koi treatments. Wide therapeutic window. Doesn't significantly affect dissolved oxygen. Generally safe for biofilter bacteria.
Calculation
Using PraziPro liquid (50,000 mg praziquantel per liter = 50 mg/mL):
Target: 2 mg/L in a 1,000-gallon (3,785 L) pond:
2 mg/L × 3,785 L = 7,570 mg of praziquantel
PraziPro needed: 7,570 mg ÷ 50 mg/mL = 151.4 mL
Target: 5 mg/L in the same pond:
5 mg/L × 3,785 L = 18,925 mg
PraziPro needed: 18,925 ÷ 50 = 378.5 mL
Using bulk praziquantel powder (typically sold as pure praziquantel):
Dose in grams = Target (mg/L) × Volume (liters) ÷ 1,000
At 2 mg/L, 3,785 L: 2 × 3,785 ÷ 1,000 = 7.57 grams
Salt
Already covered in detail in the salt dose calculator calculator, but the quick reference:
0.3% = 2.5 lbs per 100 gallons = 3 g/L
0.5% = 4.2 lbs per 100 gallons = 5 g/L
For a 1,000-gallon pond at 0.3%: 1,000 × 2.5/100 = 25 lbs of non-iodized salt
KoiQuanta Dose Calculator
KoiQuanta's built-in calculator handles all of the above:
- Select the treatment (KMnO4, formalin, praziquantel, salt, or custom)
- The pond/tank volume auto-populates from the stored profile
- Enter the target concentration
- The calculator returns the exact quantity of product to add, with the formula and safety checks visible
For formalin and KMnO4, the calculator also displays the applicable temperature safety warning and adjusts the maximum recommended dose for the current logged temperature.
For salt, the calculator shows current concentration (if you've logged it), target, and incremental addition only - preventing accidental re-addition of the full target concentration when some is already present.
Related Articles
- Koi Pond Medication Log Template: What to Record for Every Treatment
- Koi Pond Volume Calculator: Gallons and Liters
FAQ
How do I calculate potassium permanganate dose for koi?
Multiply your pond volume in liters by your target concentration in mg/L. For 2 mg/L in a 1,000-gallon (3,785 L) pond: 2 × 3,785 = 7,570 mg = 7.6 grams of potassium permanganate crystals. Pre-dissolve in a bucket of pond water before adding. Have hydrogen peroxide available as a neutralizer. Run maximum aeration throughout.
What is the safe formalin dose for koi?
Standard prolonged bath treatment is 15–25 mg/L using 37% formalin solution (15–25 mL per 1,000 liters). Reduce to 15 mg/L at water temperatures above 70°F and avoid at temperatures above 75°F without continuous DO monitoring. Formalin severely depletes dissolved oxygen - maximum aeration is mandatory. Have a bucket of clean water ready for emergency partial water changes if DO crashes.
How do I scale treatment doses for large ponds?
The calculation scales directly: multiply target concentration (mg/L) by pond volume (liters) to get the total milligrams of active ingredient needed. Then divide by the product's concentration to get the volume or weight of product to use. KoiQuanta's dose calculator does this automatically from your stored pond volume - for treatment events during active quarantine, this eliminates the manual calculation and the risk of arithmetic errors in emergency situations.
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Sources
- Associated Koi Clubs of America (AKCA)
- Koi Organisation International (KOI)
- University of Florida IFAS Extension Aquaculture Program
- Fish Vet Group
- Water Quality Association