if you take the time to read my post I didn't suggest cleaning the filter lowered the no3, but removing unwanted detrius from where ever it collects certainly does help prevent it building up in the first place. Excessive nitrates do encourage algael growth, that is without quedtion. As for waiting for a drop in flow rate before carrying out filter maintainance, well that is like waiting for your car to sieze before changing the oil filter, but each to their I guess. Mine is only an opinion ofcourse, but I do believe in regular tank management and the removal of unwanted waste.