Thank you for your question, Rony1107. In order to increase your phosphate level, I would recommend using Flourish Phosphorus. To target a specific phosphate increase, dose according to the following formula: 0.8vp=m, where v= volume of tank in gallons*, p=desired phosphate increase and m=volume of product to use in mL. For example to raise 20 gallons* to 0.1 mg/L phosphate you would use: 0.8*20*0.1=1.6 mL.
You can read about Flourish Phosphorus here: http://www.seachem.com/Products/prod...hosphorus.html
Have a nice day.