Hello
The exact cause of night leg cramps isn't known.Common causes other then low potassium levels are: muscle overextension,prolonged sitting, dehydration, diabetes, neuro muscular disorders,excessive alcohol,peripheral vascular disease.
Following helps to relieve the night leg cramps:Stretching and massaging the affected muscle,applying a cold pack to the affected muscle,taking a hot bath,using a pillow to prop the feet up in bed while sleeping on your back,supplementation with vitamin B12 & gabapentin.Also continue giving potassium.If he have a major discomfort,then I advice him to see a doctor as may need prescription medications.
Hope my answer had helped.
Doctor
Internal medicine specialist
Stretching and massaging the affected muscle,applying a cold pack to the affected muscle.Also he may consult a chiropractioner or the herbal medications.