Balancing Parameters

I was reading another post on this group concerning balancing CO2 and PO4.
This post interested me becuase algae developes on my hygrophila (sunset and
green) near the lighting, and in my filter where there is no light (?!?!?!).
However, my PO4 is around 1ppm. This, I would think, is NOT related to the
algae. However, my nitrate is always sort of on the high end of the
acceptable range; 20 -25ppm. Also, my CO2 is only around 8ppm. Reason for
algae? Filling in the blanks from the other post I was reading... If I
increase my CO2, I will lose the nitrate, then the algae, right?? Keep in
mind, this is a very heavily planted tank - becoming a garden hopefully.
Oh, and what about temperature? I keep my aquarium at 78F. OK or not?

Marty