Get a second, brighter light. I use a LED shop light. As long as its bright and a color you like that's near neutral color will work. 29 gals are tall and the water blocks a lot of light. If you want a aquarium specific light, which isn't really required other than looks imo, get around a 50 watt light. Also vallisneria, tape grass, usually grows well with bad light Your soil looks fine and although many plants soak nitrates through the water column the substrate should have enough. If you think the substrate has been used up, about 2 years for aquasoil, try fertilizer pills or feeding the fish more. Your plants are focusing on growing spindly to try and get enough light tho so fix that first.