Dosing Calculator

Litres UK Gallons US Gallons
Grams Teaspoons Tablespoons
ml
Each ml of solution adds:

Phosphorus to Phosphate Converter

If you're using a Hanna Instruments phosphorus checker (measures in ppb), use this converter to find the equivalent phosphate value (in ppm) for dosing calculations:

ppb Phosphorus =

Conversion formula: Phosphate (ppm) = Phosphorus (ppb) × 3.066 ÷ 1000

This conversion is specifically calibrated for the Hanna Instruments HI736 Ultra Low Range Phosphorus Checker.

Reference: Hanna Instruments Phosphorus to Phosphate Conversion Table (PDF)

How To Use

  1. Enter your tank volume and select either Litres, UK Gallons or US Gallons.
  2. Select the nutrient you wish to use and from the chemical it is obtained.
  3. Enter the amount of the chemical that is to be added to the solution and also if you are using Grams, Teaspoons or Tablespoons. This may require a bit of trial and error to achieve the desired ppm figure. Remember that only so much of a chemical can be added to a given amount of water.
  4. Enter the amount of water that is going to be used for the fertiliser solution.
  5. Enter how much solution you wish to add to the tank in each dose. Some people like to add small amounts at a time like 2ml whilst others like to add large amounts like 50ml. The choice is yours.
  6. Click the 'Calculate' button to display the ppm value. This is the amount that the selected nutrient will raise your tank level by.

Note: The calculator can also be used if you dose dry chemicals by putting a value of 1 in both the 'Amount of water to mix with' and 'Each ml of solution..' fields.

What ppm Values Do I Need

What amount of nutrient you wish to add depends on your dosing schedule but if dosing Estimative Index then here is a general guide:

  • 8ppm of Nitrate which is added 3x a week
  • 2ppm of Phosphate which is added 3x a week

Teaspoon Quantities

Weights used for each chemical using one teaspoon (5ml):

Chemical Weight per Teaspoon
Potassium Nitrate 6.0g
Potassium Phosphate 6.6g
Potassium Sulphate 5.1g
Magnesium Sulphate heptahydrate 5.1g
Calcium Sulphate dihydrate 4.1g
Calcium Chloride anhydrous 3.5g

Solubility in Water

Maximum solubility of the various chemicals:

Chemical Maximum Solubility
Potassium Nitrate 36g per 100ml
Potassium Phosphate 22g per 100ml
Potassium Sulphate 11.1g per 100ml
Magnesium Sulphate heptahydrate 25.5g per 100ml
Calcium Sulphate dihydrate 0.24g per 100ml
Calcium Chloride anhydrous 74g per 100ml