[Tex Gal]

Are talking about Seachem's product which is a mixture of carbon and PhosGuard? After a couple of weeks the carbon will not be active anymore and will become a great host for your beneficial bacterial. As for the PhosGuard, Seachem says it's active for at least 4 days. They do state that "Under conditions of low pH and high dosage levels, soluble aluminum can be released from alumina; at three times the label dosage rate, we detected 0.2 mg/L aluminum at a pH of 5.3." I don't know what the pH of your tank is but I might be concerned about that.

The long and short of this question is "why do it?". Your plants will need the phosphorus. After nitrogen, phosphorus and potassium are the next most needed nutrient a plant uses. The misconception that phosphates contain algae is just that, a misconception. Algae happens when a tank is out of balance. The balance is between light & nutrients. The nutrients are nitrogen, phosphorus and carbon. Water flow is important to make sure all the nutrients to all areas of the tank. When these are in balance algae can't get a good foothold because the plants will out-compete the algae for the nutrients. Seems like a waste of money to take the phosphorus out and then have to replace it again.