Child support generally doesn't depends on the current income and is determined by the court.
The court uses guidelines in determination of child support. While the judge is to determine the exact amount - you may estimate obligations using this calculator - http://www.alllaw.com/calculators/childsupport/alabama/
If your child father's financial situation changed - that is his responsibility to file a petition to modify his child support obligations.
He would need to provide his tax returns, business income statements, etc.