The particulars of your case do not give a strong argument for a judge to award split custody, but the default in Florida is now equal time sharing. Therefore, I would recommend that you get the assistance of an attorney that can help you determine the best course of action for your case. The child support for the second child is not taken into consideration with respect to your child, but the overnight visitation does. With the visitation you mentioned, it sounds like exactly 40% of overnights, which is sufficient for a modified child support obligation.
Seems to me to be a very close case that you should not be trying to handle without a lawyer. Get a good lawyer you can work with and follow his/her advice.
This is for informational purposes only and is not legal advice upon which anyone should rely. Nor does it create any attorney client relationship.
Stanton L. Cobb
Board Certified Marital & Family Law Specialist
Fellow - American Academy of Matrimonial Lawyers
P.O. Box 149223
Orlando, FL 32814-9223