The pH range of a solution affects the absorption of nutrients. It is therefore recommended that nutrient solutions have a pH of between 5.4 and 6.0, as this is the range within which nutrients are best absorbed. Citric acid is an organic acid which, once dissolved in water, has no EC value. Citric acid is used for flushing away old fertilisers from substrates between rounds of cultivation, among other applications.
Citric acid contributes to the activation of ADP and ATP carriers in plants. It is therefore preferable to use citric acid several times at the start of each crop. ATP and ADP (adenosine triphosphate and adenosine diphosphate) are energy carriers that transport the energy in plants.