Hey EK on your phosphate test did you just do it out of the water column. If so can you do one right on top of the sand bed, its ok if a particle or two goes in the test vial, also go to the LR where you have some cyano brush it off and do another test vial right at the surface.
Here is the thinking behind it EK. Lighting is eliminated, flow is a bit of a concern but will not do it on its own. Your phosphate kit is reading .25 in regards to inorganic phosphates, thats not good. Inorganic phosphates are usually bound up by organics quickly after entering the tank, if your still showing them, that would leave me to believe your organic phosphates are really high and cant consume anymore. Since you have lessened your feeding (thus your source) and still have it, we need to find the source of them. Removeing the cyano from a spot on the sand and on the rock will tell us if the source is the sand and/or the rock.
Let me know and we can go from thier.
Ps. Curt on the binding of Phospahte in the argonite, this is true but it will only bind until its full then stop, so if he is still getting readings tat would mean that the rock is not absorbing anymore, thus it would seem to be more of a biological cycle then that.
Mike