Triple Super Phosphate is made by the action of phosphoric acid on raw rock phosphate [also called Appatite]. It typically contains 46% phosphate, soluble in neutral ammonium citrate and water. Of this, typically 90% is soluble in water alone. Because the phosphate on TSP is never completely water-soluble, it cannot be used in the manufacture of clear-liquid fertilisers.

Bunns offer the best quality TSP. If you are offered cheaper versions of Triple Super Phosphate, make sure that:

• It actually contains 46% neutral ammonium citrate and water phosphate. 'Cheaper' triple can sometimes contain as little as 40% owing to high concentrations of impurities
• The water-solubility is at least 90%. 'Cheap' Triple can sometimes have low water-solubility, for example 75% or lower.