do you happen to know if 54watt T5HO doesnt come in 36"?
Unfortunately they do not, 54w bulb are 4 feet long. Why do you want a 3 ft light fixture? The tank should be 4 feet long if it is a 110 tall.
Three things concern me:
1. CO2 being on the same hours as the light. It should turn on before the lights to allow for levels to rise before lights turn on.
2. Lack of dosing for major nutrients.
So I'd say its a nutrient and CO2 issue and not lighting.
These are great points. It is certainly possible the plants have some sort of nutrient deficiency. Unfortunately this particular species is not a good indicator plant for most nutrient issues (except for iron deficiency which the plants do not have). Without seeing signs of problems in the other plants (particularly broad leafy stem plants) it is impossible to say if it is a lack of nutrients.
If the other taller plants are growing normally, then it is unlikely to be nutrients. But if there are damaged sections then you should post close up photos of the damage so we can see what it might be.
I do find it strange that 4x39w T5HO do not produce enough light to grow the micro swords. It might not be perfect lighting, but one would think it at least reaches the bare minimum, even in such a deep tank and with a 3ft fixture on a 4 ft tank.
I think the cheapest way to figure out this problem is to post more photos of your other stem plants, then start dosing macros as dmagerl suggested wait a week and see if the plants are responding with new growth. If not then it is likely the lights.
I still think it looks like lighting problems due to the color/shape of the plants. They aren't really growing at all from the looks of the picture and few deficiencies outright stop plant growth in its tracks like that. A lack of light on the other hand does cause plants to halt their growth.
How far above the tank are the lights positioned? Are they resting on the rim or elevated?
What brand of lighting are you using and are there individual reflectors around each bulb?