to prepare nutrient solution | Hydroponics | GEEKGARDENER

Hi all i have bought a readymade npk water soluble fertilizer in the ratio
19:19:19.the company name is nagarjuna peek with essential micro nutrients.the
shopkeeper told to use 7.5grams/litre of water.but i have  a doubt it is for
soil.can anyone tell me how much i should use per litre.if i am to use it for
growing tomato in cocopeat.

thanks in advance