Yeah arowana’s are known to be jumpers, in nature they jump out of the water to catch prey. We had one at one point and it did exactly as you described, very fast and loved to jump.
Gorgeous flower horn though! I’ve dealt with ich a few times… always after adding new fish. Always had good luck with the API ich cure+crank the temperature, only problem is you have to remove your activated carbon in your filter and it turns the water a wicked shade of green.