This is what Fenner says on his web site........
"" This "trick" involves "over-driving nitrification" temporarily by providing a ready (and safe) source of carbon... in the form of a monocyclic/simple sugar. The best is Glucose (though lactose, galactose, fructose... others might be used). A small solution of about a gram per fifty gallons (doesn't take much) is made in some freshwater and this added to the system toward the evening/dark time... once a week for about three times. Takes a few days to weeks to show effect, but generally useful. Bob Fenner......""