My understanding, (mostly from Tom Barr's vast knowledge he's shared),
is that phosphate by itself does not cause algae. A lack of phosphate
will retard plant growth.

To simplify, here's the formula for planted and non-planted tanks.

Non planted:
Use very low amounts of light for short durations during the day.
Change water with enough frequency to limit nitrates to no more than
20ppm.
If your water supply is high in phosphates, the absorber can't hurt.

Planted tanks:
Cover the bottom of the tank with plants.
2wpg or more for 10-12 hours a day.
Add C02 at 20-30ppm
Monitor nitrate levels. Dose a small amount of trace elements and
potassium when nitrates are present from fish food.
Begin dosing KNO3 along with K and traces when the plants start using
all the fish food induced nitrates. At this time phosphates will also
be used up, so start dosing them in small amounts too. With 40-50%
weekly water changes, try to maintain NPK in this ratio of ppm: 8:1:16

steve