.3 to .03 is a large jump, id just test p04 with the instrument twice a day just to make sure it doesnt run to 0. Every tank is different, i wouldnt even run rowa in my red sea tank, a tablespoon is good enuff for me. My nano needs tons of rowa for unknown reasons. Maybe its the rock, not sure. The thing with gfo, you have to find your tanks "medium". Takes alot of testing, alot of patients, alot of gfo lol but its like dosing, you have to find the exact amount to work good mixed into your feeding+maitnence regiem