Father Responsible for paying mother child support

by Mac
(Colorado)

I divorced my ex in 2009. At the time we got joint custody in Douglas County, Colorado. The kids were ordered to attend school where the mother lived and because my income was greater (hers was $0 at the time)I had to pay $1600 for 4 children.

Issues arose later in 2009 and I took my oldest daughter back temporarily before it was agreed for her to stay with my Father and Step-Mother all in 2010 onward.

The only modification to child support was to account for the mother finally getting a job reducing support to $1200.

However, she does not provide any money back to my Father for raising our oldest daughter. He doesn't care who, but wants either myself or my ex to pay him support.

Can I reduce the amount of support to my ex to say $900/mo and pay the other $300 to my Father since he is the one raising her and paying all of her expenses? (She doesn't get as much as little gifts like her brother and sisters do because "she doesn't live with her mother")

Thanks