A final divorce decree providing for the custody of a child can be materially modified only if: (1) there are facts concerning the welfare of the child that the court did not know at the time the decree was entered, or; (2) there has been a change in circumstances shown to have arisen since the decree. Belford v. Belford, 159 Fla. 547, 32 So. 2d 312, 314 (Fla. 1947). This rule promotes the finality of the judicial determination of the custody of children. After the trial court enters the original final judgment decree, it is res judicata of the facts and circumstances at the time the judgment became final. Thus, there is a presumption in favor of the reasonableness of the original decree. Id. This presumption may be overcome when changes in circumstances have arisen which warrant and justify modification of the original decree. See In re Gregory, 313 So. 2d 735, 738 (Fla. 1975); Frazier v. Frazier, 109 Fla. 164, 147 So. 464, 466 (Fla. 1933). To modify such judgments, the trial court must decide whether there is a "factual basis sufficient to show that conditions have become materially altered since the entry of the previous decree." Id. at 467. The degree of change in the conditions and circumstances since the date of the previous decree must be of a substantial character. Bennett v. Bennett, 73 So. 2d 274, 278 (Fla. 1954). In Cooper v. Gress, 854 So. 2d 262 (Fla. 1st DCA 2003), the First District held: The posture of a modification proceeding is entirely different from that of an initial custody determination, and the party seeking to modify custody has a much heavier burden to show a proper ground for the change. The trial judge's personal observation, stated in the record, that rotating custody arrangements never work, does not justify modifying the custody plan, absent a substantial change of circumstances resulting in the modification's being in the children's best interests. Id. at 267.