If, like me, it is easier for you to dose your NPK by mixing it with water in advance (useful for those of us with smaller tanks, anyone else here struggle to visualise 1/32 of a teaspoon?!) here is what I believe is a teaspoon based measurement for 500ml water mixing: KNO3 - add 6.25 level teaspoons (or 6 and a little bit more!) to 500ml of water KH2PO4 - add 3.125 level teaspoons (or 3!) to 500ml of water K2SO4 - add 7.81 level teaspoons (or 7!) to 500ml of water I use 250ml bottles so I just halfed (roughly) the amounts above. I only add 10ml of KNO3 3x per week for a 250ml bottle lasts me 25 doses which is ~2 months. I haven't weight checked these, I worked it back from the teaspoon/ml ratio on theplantedtank.co.uk and it appears to be about right from when I weight mixed. I don't have my own scales to measure 0.1g increments and have to borrow them from work. I managed to forget and forget to borrow them before my KNO3 ran out so had to work them out as above. I dose trace via Tropica Plant Nutrition so didn't work this out. If it seems right it should be easier for newcomers without scales and perhaps for those who have scales but can't be bothered weighing things each time they mix ferts! If I am wrong in the ratios please correct me!