How long has the tank been set up? When the tank is cycling you can very easily have spikes in Ammonia, Nitrite and nitrate. Once nitrites and ammonia are 0 and nitrate's are showing up, between 10-40 then your tank is cycled. This process (from the time you set up the aquarium) can take up to 6 weeks.
From what I've heard, the best way for these guys to answer a deficiency question is to take a picture of the plants with the problem.
Only thing I can see is that you're dosing nitrates .. it'd cause a spike if your plants aren't absorbing it. Maybe cut back on those a little?
I'm still new to the game. I'm sure someone who is more experienced will come along shortly and offer more information.
as for the light, it sounds ok to me. Do you think you can run a t8 instead of a t12? It'd save a bit in energy costs. The bubls run $8 for 2 at lowes/homedepot ..