I'm trying to raise my phosphate from zero, it has always been undetectable. It sounds like it is just binding to my reef saver rock. I mixed up a TSP solution and 4mL should have raised it to 0.01ppm. I added 4mL over an hour and then tested 30 minutes after. It was still zero. So I did it again (should now be at 0.02ppm) and still zero. Before I started I did a test with a gallon of tank water and few drops of my mixture and it went from zero to 0.04ppm, so my test seems fine. Is there any harm in continuing this until I reach a detectable level? Obviously not adding it really fast or a bunch at once, but faster than 4mL per day and then it might take a month to reach equilibrium. It seems that if I'm adding it and it almost immediately binds then there wouldn't be any harm in adding more. Maybe cap a daily dose at 20mL (should be 0.05ppm), but test after each 4mL dose.