Meaning of ADD in English
BAD : The other ingredients are then added into the mixture.
GOOD : The other ingredients are then added to the mixture.
add sth to sth (NOT into ): 'They are demanding that a new clause be added to the contract which will give them a share of the profits.' 'When a prefix is added to a word, you make a new word.'
Longman Common Errors English vocabulary. Английский словарь распространенных ошибок Longman. 2012