Get ya some powerful pumps and point them at the bottom of the barrel in between the rocks. Mags 9.5 or 12s, or the like, work great... or whatever you have laying around.
With my phosphate experiments with Dr. Holmes-Farley, I learned that salinity and temperature matters. If you need to soak up some phosphate with LC, then 78-80 degrees and 1.026 will work best... the stuff will unbind best in the conditions that it was bound, is what I learned, IIRC. You don't need to heat it to let bacteria go to work, just for maximum phosphate removal.
With my phosphate experiments with Dr. Holmes-Farley, I learned that salinity and temperature matters. If you need to soak up some phosphate with LC, then 78-80 degrees and 1.026 will work best... the stuff will unbind best in the conditions that it was bound, is what I learned, IIRC. You don't need to heat it to let bacteria go to work, just for maximum phosphate removal.