DIY Fertilizer for a Freshwater Planted Aquarium

Put down a 2-inch layer of an iron-enriched substrate, such as fluorite, in the bottom of your aquarium. Cover the substrate with another inch or so of regular aquarium sand or gravel. The iron-enriched substrate will help to keep the roots of your aquarium plants healthy, and the fertilizer you add to the water will encourage plant growth.

Fill a 2-liter plastic bottle with distilled water to use as the base for your fertilizer.

Add 61 grams, or about 11 teaspoons, of potassium nitrate (KNO3) to the water in the bottle and agitate the bottle gently to distribute it. Potassium nitrate is also called stump remover and can be found at your local hydroponics store or ordered online.

Scoop about a teaspoon, or 5 grams, of potassium monophosphate (KP04), also called fleet enema, into the bottle and agitate the bottle again to distribute it.

Add 10.8 grams, or about 2 teaspoons, of magnesium sulfate (MGS04), otherwise known as Epsom salts, to the mixture.

Finish the mixture by adding a small amount, about 1.8 grams or 1/3-teaspoon, of potassium sulfate (KS04).

Agitate the bottle to mix the solution or insert a long straw or wooden skewer into the bottle to use as a stir stick.

Pour some of the mixture into a small plastic dosing bottle. You will continue to use the 2-liter bottle for storing your fertilizer, and the dosing bottle will be used to dose the tank.

Squeeze about 5 ml of the fertilizer solution per 10 gallons of tank water three times a week into the tank. If you have a 20-gallon tank, you will squeeze in 10 ml of the solution each time; and if you have a 50-gallon tank, you will dose the tank with 25 ml of the fertilizer.

Test the water in your tank regularly with a water chemistry test kit to check the nitrate levels. If the nitrate levels get too high, reduce the dosage of the fertilizer or the frequency with which you dose the tank.