How tall is the tank? My 100 gallon is over 30" tall. That amount of depth from top to bottom requires more light to be able to penatrate to the bottom of the tank.
C02 will also be a big factor. I would never use Excel in a tank that big. The tank is too big for it to be really effective.
Flourite provides iron and thats it. If you had a soil based tank and followed a low tech method as outlined by Diana Walstad, an organic based soil provides nitrogen and trace minerals as well as C02 from the organic material and bacteria.
Robert Paul Hudson
RAOK Club #1
Kindness like love is unconditional