Ex asked if can claim 1 child as an eligible dependent. I am married. He is single. They go weekends. Is this ok if I have full custody? Can I claim the child for CTB?

Two children with ex. i've been claiming them both since born. I did claim oldest as equivalent to spouse a few years ago before re-married. Now ex wants to claim. I have full custody, but they go there 3/4 weekends a month. If ex is claiming eligible dependent amount, can i still claim the same child for child tax benefits and all other deductions? 

After you file

From the info provided, your ex does not meet the qualifications for claiming the eligible dependant amount.

1. You have full custody so you're considered to be supporting the child.

2. The child lives with you.

These 2 facts disqualify the Eligible Dependant claim by your former spouse.