it looks like a deficiancy of some sort or too much water, im not a plant doctor anything but my opinon im guessing it could be a couple things. Could be watering... 20oz of water every 4 days?
so are saying that he only feeds every 4 days? or that in a total of 4 days it gets 20oz of water? when i water i just stick my finger in the soil an inch deep and if its pretty dry ill give it enough to soak about 4 inches deep. i do it by guesstamating but maybe tell him to get a moisture meter if he dont already have one. then i wait again til it dry's and just repeat and leave it up to the plants to show me how much there drinking. if you leave the roots to dry up in the soil to long theyll shrivel up and and die but too much water you can get root rot which is pretty self explainatory lol either or will cause your plant to look shrivled.
so you just gotta find a happy medium between the plant and planter
What kinda lighting is it? cfls? mh? how much does he have or how does it put out? how many plants are under that light? some plants are greedy and steal the spotlight, leaving the others to sit in its shadow and die
hope this helped or gave you some questions to think on