Yeah. I started watching his second video and he started talking about need to use pellet food and I thought "you gotta be kidding me he was feeding live meal worms and didn't know about pellet food?".Yes indeed, Flowerhorn are quite prone to intestinal disorders -- I've seen that and other videos by that YouTuber and imho while the temp change during his water change might have weakened the fish to the degree that it enabled HITH to take over, imho he also went overboard on the crazy variety of foods he was trying to feed his fish. All a Flowerhorn needs is a good quality pellet or two and maybe only very occasional treat of frozen foods (and arguably not freeze dried krill, which some say can scratch their stomach lining, but personally not sure on that point).
It was interesting that he would video all this stuff he did to his fish.
Sounds like with flowerhorns a good bit of study is in order before keeping this fish.