Young's Literal Translation for a messenger at a set time was going down in the pool, and was troubling the water, the first then having gone in after the troubling of the water, became whole of whatever sickness he was held.
Holman Christian Standard Bible because an angel would go down into the pool from time to time and stir up the water. Then the first one who got in after the water was stirred up recovered from whatever ailment he had.