yes if you do 90-100 % change then you add 10 ppm Ca and 4 ppm Mg, afterward every time you do any 50% water change, you add 5 ppm Ca and 2 ppm Mg.I said that I did a big water change, I targeted 10ppm ca 4ppm magnesium like 90 percent, I will do a 50 percent water change this week. Isn't my 5ppm ca 2ppm magnesium target correct? Sometimes if I wait 2 weeks and do a 50 percent water change and aim for 10ppm ca 4 ppm magnesium, would it be correct?