LOL!!! I dont have the calculator in front of me but i thought the amount sounded a bit high. Recalculate it to 4ppm- 5 is a bit of an overkill. 5mls=1teaspoon but do not use a regular teaspoon to dose, use an actual measuring spoon because its a bit smaller than regular 'teaspoon' in the kitchen drawer. This where a 5ml syringe really helps for accuracy-this stuff is POTENT (do not sniff the bottle, it will knock you on the floor!) so round the any 'in-between' amounts down. You then can wait 15mins & test your tanks amm levels. If its not quite 4, its easier to add a little bit more than dose too high & have to do a big water change! I did this test before & i dont recall the exact number, but its something like 15-20drops of liquid in 1ml if this helps for smaller amounts. Happy dosing & keep us posted!