"I'll always remember your stoke when we'd shoot, skate (and) surf and how much hope you had for your future.
"God bless the family and extended family that were always there for you."
David, who also competed professionally in skateboarding, had suffered from multiple seizures in the past.
In 2016, an episode caused him to fall heavily while skateboarding at a park in California.
And later that same year, he suffered a six-hour seizure that nearly took his life while at home in Oahu.
He underwent surgery in early 2017 to remove a muscle that had grown on his heart, which was causing the seizures.
Australian surfing legend Mick Fanning paid tribute to David on Instagram: "Far out that's heartbreaking.
"He was a great kid. That's really sad. I remember him coming round to our Red Bull house in Hawaii as a 12-year-old and I was cooking a barbecue.
"Gave him some food and he automatically did the dishes without having to ask, but was classic at that age.
"He'd come check in most nights to see what was on for dinner, hoping it was another barbecue — haha always enjoyed chatting to him."
Eleven-time world champion Kelly Slater posted: "Kalani was one of the most talented ever surfer/skaters on Earth, constantly pushing the limits every time he was on his feet.
"Condolences to the huge community of friends Kalani had coast to coast and across the globe."
