Maybe it's not algae
 

After I started using CO2, my parameters became perfect with PO4 = .1, and
NO3 = 10ppm. However, what I originally thought was algae has not been
effected. When my green hygrophila grows to ~7" below the lighting, the
leaves turn light brown, then the plant turns sideways and keeps growing so
that the stem is going across the tank instead of toward the lighting. It
does not rub off, is not slimy, and the algae eaters (ottos) have no
interest in it. There is no visible algae anywhere else in the aquarium.
In fact, I even supplement algae tablets for the ottos. So here's a
question... Is it even algae? Perhaps I have too bright of spectrum which
is burning the plants. Possible? Here's what I have - 20G High (16"- 3"
sand), 2 Coralife Day-Max 15W, 1 Coralife NutriGrow 15W, 1 Hagen Aquaglo 15W
(Yes, I know this one isn't the problem).

Marty

Maybe it's not algae
 

Too much light can bleach leaves - it happens particularly with Ceratophylum
demersum - the whorls of leaves become yellowish-brown in colour and have a
bleached look (completely washed out). They look like they are dying off.
You may not be burning the plants but you may be causing them to lose the
chlorophyll that they need for energy an give the plant its green colour.

Try switching one of the light off especially where the Hygrophila is
(probably background) and see if the plant responds differently.

Martin