I do not think because of fertilizer dosing. I'm dose 10ppm of NO3 3 times a week, 1.5ppm PO4 3 times a week and Seachem trace 3 times a week. I do not think because of CO2. CO2 should around 30ppm according to the drop checker.
Some qustions in my mind:
1. Could it be because of the substrate? I'm using ADA Africana, If I'm not mistaken it is the least fertile from ADA soil. Does Utricularia graminifolia need very fertile soils?
2. Could it be because of light? I'm using 36W PL light, should be enough but the moss probably over shadow it.
I decided to trim the moss, hopefully Utricularia graminifolia will get better light and grow better. It is about time to trim the moss anyway.