Mark Trueman wrote:

Might not be co2, may be light.

Then again, it might be the Flourite.

We're not going to reesolve it here. Dustin, Rotala macrandra grows pretty fast.
Adjust the light, see what happens in the two substrates. My R. macrandra grows
very very red and 1-2 cm per day with 3WPG, 25ppm CO2 and 100% flourite.