My magnesium was at 1160ppm. I got fluval magnesium. It's a 30 gallon total water system. My question is how much to dose of the product. It's says Add 5 mL per 75 L (20 US Gal.) once a week. Weekly dosage provides 5 mg/L of magnesium. How much would I need to say raise my levels by 10ppm.thanks in advance