An update:
I have installed an inline CO2 diffuser 2 weeks ago (CO2 Art) and now I have no doubt that the CO2 is being properly distributed. However, the growth in the Rotala Rotundifolia is still not healthy.
A minor portion of the stems does look healthy, however the majority continues to show stunted growth.
Any suggestions on what the next steps should be in trying to clear out this issue?
Is this new stunted growth, and did you cut off the old previous stunted growth? in my experience once a stem starts stunting it won't revert back unless the stunted growth is removed allowing it to put out fresh shoots.