the theory behind adding sugar is that the bacteria hv plenty of surface area, nitrogen and oxygen to work, but the limiting factor is carbon..
so by adding some sugar, u can give that boost to the bacteria, as it contains plenty of carbon..
the prob is, its so effective that there will be a bacterial bloom, the bacteria will multiply super fast..
hence u get cloudy water, and oxygen will be used up v fast..
so must add a bit at a time, plus hv strong aeration, then this method can work..