How long should we leave the lights on in our aquarium . . .?

I have a 55 gallon tank with 1 pleco (about 6"), 1 Catfish (medium-ish) and 2 small-medium cichlids. We seem to constantly have water issues mostly with algae. My husband did a test strip & everything seemed fine after the most recent water change & conditioning. But now the algae is coming back & one of the coral ornaments is almost black. Could this be a light issue? And if so . . . how long should we leave the lights on? My husband gets up around 4am, turns it on & feeds them. I just now realized we don't turn it off until around 10pm normally. Could this be the problem?