Roots wanna have as dark as possible. And not too warm above 28C . Additional oxygen with piezoelectric air pump or fill the cups with porous granulate perlite for example or very simple try to keep the root containment as closed as possible for high humidity inside and fill only 1/3rd at max (N-P-K 10-5-10 solution 1g/l). If there are more roots it could even be lowered to maybe an inch of liquid nutrients.