What determines if and how much child support would be increased in Texas?

From my understanding, a custodial parent can request a review of the non-custodial parents child support payments every 3 years. If there is an increase in income, also taking into consideration any other dependent children of the non-custodial parent, the state would increase the child support. I am not sure on the amount of the increase in income that has to happen in order to change the order. I mean, if a father is bringing home $30,000 and child support is set on that, and then 3 years later his ex requests a review and he is making $31,000 then would that be enough of an increase in income to increase the child support, or does there have to be a significant increase in the income? I am just trying to get my facts straight before speaking to my ex. I didn't request a review until 9 years later and he had had such an increase in income, that the state raised his child support quite a lot. He called me money hungry and said that money was all I cared about.