Are you legally gettng access to his bank account? if so, print out the last years bank statements and contact either an attorney or support enforcement for your county. You can prove his income and there should be no issue, he will have to prove the deposits are not income related (same thing happened to me)
If you are obtaining the bank records illegally (if your name is not on the account it is illegal) then you will have to get a court order to have the bank account records supeonea. Once you get the court order you can then enforce it at the bank and having them print out all of the bank records and copies of all of the deposits, they can prove where the money came from by the number listed as the depositing institution..
The results will be the same but the method you need to use is different as you can not obtain bank information illegally. Once you get the information The take the information to support enforcement for a review of his child support case.