Kuhlis aren't picky about specific parameters, as long as they are stable, the tank is cycled, and it gets regular water changes.
The thing that comes to my mind regarding these 2 fish together is the size difference. Although clowns grow slowly, their adult size is like 2 feet.. Kuhlis stay 3-4 inches. Also clowns are quite rambunctious and kuhlis can be pretty timid. They can be frightened by larger fish and are out competed for food easily. If a kuhli is eating a wafer and a larger fish swims up and tries to take a bite, it will swim away and hide.
20 gallon high-tech planted