i am looking at trying Brightwell Aquarics Phosphat-E. The bottle says 1 ml will remove 1ppm of phosphate from 4 gallons. I have a 100 gallon tank with .1 phosphate. If I add 1.25ml 1 time that should drop my phosphate to .05. Is my math correct? What’s the best way to add this? And how often should I add it?