lowering po4 levels

I want to lower my po4 dosage in my 55 gal./high light tank. I am currently dosing 2 ppm. every other day.I want to know if I add 1 ppm instead of 2 ppm, will this be enough to be sure the po4 will not bottom out before adding more? How much on average does po4 get used up provided nothing else is in limmited quantities? Thanks for the help,
John

 

Re: lowering po4 levels

Two weeks ago I tested my po4 at weeks end, with a calibrated kit, and the level was 5 ppm. Last week I kept the po4 level at 2 ppm consistently and I noticed a dramatic decrease in green spot algae. It was not completely gone, but was alot less at the end of the week. Now I know one week is not enough time to draw any real conclusion, but there was still a noticeable change in the gs growth. I should also add that in this same week, I switched from csm+b to flourish and started adding 2 mls. of flourish iron every other day. Could these other changes account for the gs lessening?
This week I am goig to keep po4 levels at 2ppm again and see the results.If I get the same results, I will change back to my old po4 dosing routine(2 ppm every other day) with the addition of the flourish and iron to see if that makes any difference.Any comments on this idea? Thanks,
John