I'm confused, got two tiger oscar fish. woke up.one night w splashing both were white, Wat cud it be? t?

At night I turn my tank off but as soon as I turned it back on their color got back.n they started swimming normal... I freaked. Read bout neon tetra n got suggestions on water temps.... but wen i barely tured d light on they looked pretty bad, floating almost, complications swimmin....Wat cud this be?? Wat shud I do....