Dude, just go to drugstore and buy fleet enema. It's cheap and easy to dose. I tested it with the original bottle (the squeeze bottle and tip). 1 drop will increase 0.1ppm of PO4 for each 10gl of water. So in your case, 3 drops will increase 0.1ppm PO4 in your tank. NOte that their drop size is smaller than standard dropper.