Kulow, who hadn't lowered his 100 free PB in long course since 2021, took off more than a second on Day 2 in Mission Viejo, clocking 49.29 in the final.
McFadden's swim from prelims was just 0.12 seconds off Aaron Shackell's national HS record time of 1:32.85, and he still has a shot at the record in finals.
At last week's Pro Swim Series stop in Knoxville, 17-year-old Henry McFadden stunned the field with his closing speed on the final length of the 200 free.