Don't let the title fool you - this is a good read
Looks like you need to know your PO4 level, then go from there
http://www.theaquariumsolution.com/r...ste-your-money
Forgot to add this link
http://www.theaquariumsolution.com/r...ty-information
If you can't convert the mls to grams, use a measuring cup and measure mls
What is your PO4 reading right now ?
500ml removes 3ppm in 500g - so do some math based on that