One can not remove from the water that which is not in the water long enough to remove. If your nutrients are being tied up by living matter at so fast a rate as to not be detected then they will not be in the water long enough to skim out or remove through water changes. All your nutrients are being tied up in the organic life forms in the tank. If you choose to kill them through light deprivation then the nutrients will be dumed into the water stream and can be removed. By stopping or limiting inputs of nutrients you will, stop their growth but not kill them as the first organisms to starve and die will be the nitrifying bacteria which will dump nutrients into the water to be quickly taken up by the algae. Is is obvious if you kill the nitrifying bacteria off that even their released nutrients will not be removed by water changes and skimming as if it isn't already working then it still will not work just be cause your trying to starve the algae. The tooth brush and siphon hose makes sense but removal of the rock and a vigorous cleaning would make more sense. Most things being mentioned will only help the problem from coming back once it is cleared up, but there is little being brought up that will be very effective at solving the existing problem now. IMO If you look at ocean pictures or read about micro, macro algae and Phytoplankton, even cyano bacteria you will find that in general nuisance and most macro lagae will not grow at depths where the chief light waves are in the blue actinic wave lengths. You can light your tank with actinic blue at or around the 420 nm rwave length and invertebartes and fish will di=o fine for weeks, but nearly if not all nuisance algae will die. Even Bryopsis requires lighting above 500 nm.