Coetzee qualified for the world juniors in the 100m backstroke, but also in his favoured stroke, the butterfly, where he is the top New Zealand junior in the 200m, with a personal best of 2.02, and he is a 400m individual medley gun.
"It's going to be a good experience at the junior worlds. I'm going to go in there and not worry about it, focus on my own race, and try to beat my own goals," says the South African-born Coetzee, who came to New Zealand when he was a toddler.
Those goals include making the semifinals, at least, and he acknowledges the strength of the Australians and Americans.
But a week later in Samoa he is keen to make a statement and win gold, albeit among weaker competition.
All this intense swimming will be a priceless lead-in to his major goal, which is to qualify for the 2016 Rio Olympics. What are his chances, given that his PB for the 200m fly is over five seconds outside the qualifying mark?
"If I keep tracking like I am, and taking off the seconds, I can realistically get there."
In the meantime he'll be staring at the bottom of the Millennium Pool for eight sessions a week, plus two in the gym, racking up the mileage required of a middle distance swimmer with lofty goals and the well-honed engine to meet those goals.
Sometimes he is late for school because of the distance from Orewa to Mairangi Bay, and he refuels on the run. But he manages his time well and will have his laptop on his travels.
Coetzee loves the butterfly, that awkward-looking stroke so beloved of the great Anthony Mosse.
"I enjoy it because of the difficulty of the stroke. Not everyone can do it.
"Butterfly mileage makes up a lot of the swimming work I do. You learn to love the stroke you choose," he says, confessing a dislike for breast stroke.
Coetzee pauses when considering his strengths as a swimmer. Technique is vital, and Ansorg helps him hone that. But you cannot coach that inner drive.
"I have the determination to go through and try to win the race, no matter how far behind I am. But I do need to work more on my skill.
"When I race the New Zealand Olympians, they beat me on the underwater, and these are the things I am working on."
As he says, you need to follow the processes. He'll be doing just that through an intense August and September.