anubias turning yellow

My plant tank has been set up for roughly 7 weeks.  All the bunch plants and 
swords are doing well.  However, despite the fact that they are growing new 
leaves (two have also produced flower stalks), the anubias leaves are turning 
yellow. The new leaves are also quite yellow, and don't appear to be turning 

The anubias are an assortment of nana, barteri, coffeafolia, bangkok, and 
congensis.  The nana and bangkok appear to be suffering the most.  All were 
bare root and I assume grown emersed.

I use Dupla fertilizers, and maintain iron concentrations of .1 to .2 ppm.  GH 
is 3, KH is 3.5, and I use CO2 to maintain a pH of 6.8 - 6.9.  I do weekly 30% 
water changes with RO water reconstituted with 1 tsp/10 gallons synthetic sea 
salt and calcium carbonate.  My well water has GH of .5 and KH of 24, so I 
don't mix any tap water with the RO.  Nitrates and phosphates are undetectable 
in the tank and I wonder if the anubias are suffering from a lack of nitrogen.  
There is a fairly large fish population and I feed well so my assumption is 
that the hygro and other fast growing plants are consuming all the ammonia etc. 
that is produced.

Is this normal for emersed grown anubias, or is it possible that the lack of 
nitrogen is responsible?  If it is a lack of nitrogen, what would be an 
effective method to increase the level?  I skipped the water change this week 
to see if the nitrate level would increase a little.