If he gives his second wife the cost of tuition fees, is he obliged to give the same amount to his first wife?
Question

                I am married and I have three children. I took a second wife in secret, then my first wife found out about that later on. My question is:

How can I treat them equitably? Should I give the first wife what I gave to the second of gold, clothing and mahr (dowry)? From what time should I start to treat them equitably? How should I do that when the second wife is studying at University, and every day I give her the cost of tuition? Should I give the first wife the same amount?
Praise be to Allah.
    Islam 
    has made it incumbent upon the man who is married to more than one wife to 
    treat his wives equitably in terms of spending on their maintenance. Equity 
    in this case means spending on them according to his means, and giving each 
    of them what she needs of maintenance and clothing, that is usually given to 
    women like her. Based on that, one of them may need things that the other 
    does not need in terms of maintenance. One who is studying may need, because 
    of her study, things that the one who is not studying does not need. One who 
    is pregnant may need maintenance that one who is not pregnant does not need. 
    One who is sick may need things that the one who is not sick does not need, 
    and so on. 

    The 
    point is that he is obliged to treat them equitably in terms of maintenance, 
    so as to suffice each one of them. With regard to anything more than what is 
    sufficient, he is not obliged to treat them equitably in that regard. 

    Ibn 
    Qudaamah said: 

    He 
    does not have to treat his wives equally in terms of maintenance and 
    clothing if he has done what is obligatory in the case of each one of them. 

    Ahmad 
    said – concerning a man who had two wives: He may favour one of them over 
    the other in terms of maintenance, intimacy and clothing, so long as the 
    other one is provided for sufficiently. He may buy a garment for one that is 
    more expensive, so long as the other one is adequately clothed. 

    That 
    is because equal treatment in all these matters is difficult, and if it was 
    made obligatory, he would not be able to do it except with great difficulty. 
    Thus this obligation is waived, as in the case of equal treatment in terms 
    of intimacy.

    End 
    quote from al-Mughni, 7/232 

    
    Al-Haafiz Ibn Hajar said: 

    If he 
    has fulfilled his obligations towards each one of them in terms of clothing, 
    maintenance and spending the night, then it does not matter if he inclines 
    more towards one of them or gives a gift to one of them.

    End 
    quote from Fath al-Baari, 9/391 

    For 
    more information, please see question no. 10091

    Based 
    on the above, what you must do is treat them equitably by spending on each 
    one of them that which is sufficient for her. You do not have to give the 
    first wife what you spent on the mahr and then on clothing and gold for the 
    second one. 

    And 
    Allah knows best.