Though lions don't appreciate fast swings in temperature, they have enormous range tolerance. I have 'found' them in forgotten tanks at wholesalers in incredibly saline water, so much they should have been floating on top. A super-commonplace problem with 'lion tanks' is the loss of alkaline reserve with over feeding, inadequate filtration, infrequent water changes. The scenario goes like this. Water quality tanks, with pH diving dangerously below 7.6, lions go into hiding, breathing heavily.
Owner calls service company complaining.
Needs be capable of handling occasional large amounts of solid waste and efficient to keep ammonia and nitrites low. In the ancient days of marine aquarium keeping some writers advocated using lions instead of damsels for establishing nutrient cycling. Which leads us to, tah-dah, lighting. Make it subdued, low illumination flourescents, at least a dark corner. Very willing to share living space with their own and other lionfish species.