GFO should not tumble. At most, the very top layer should just barely very gently boil. Tumbling causes friction between the granules which will produce GFO dust that will go into your tank. For the same reason, you don't want carbon to tumble either.
Skimmer King makes a good point about waterchanges not being very effective in lowering the amount of nutrients in the water column although he has interesting math.
Also, the rock and substrate will leech more nutrients any time the water column has less nutrients than them.
Waterchanges are important though as you should be manually removing as much algae as possible during waterchanges as well as siphoning/vacuuming out as much detritus as possible. Algae holds nutrients within itself so manual removal of the algae not only removes the unsightly algae it also removes those nutrients bound up in the algae. If you simply kill the algae when the algae dies those nutrients go back into the water column where they can feed new algae. Detritus is solid nutrients which can't dissolve into the water column if it is siphoned out soon enough. Powerheads should be placed to help prevent detritus from settling.