Hi
How about adding some fertilizer? Your description sounds to me like it is starving.
Plants need light, CO2, N, P, K as macro nutrients and Fe, Mg, Mn, S, B, Co, Li, Cu, I, Mo, Ni, Sn, F, Al, Zn, ... as trace nutrients to grow healthy.
If you can't does enough of a nutrient like CO2 you can reduce the light a bit to limit the need of the plant and keep it alive this way.
Regards,
Dominik Riva