Dupla fertilizers

Recently, I began using the Duplaplant 24 fertilizer daily in my 100 
gal tank.  I started with 6 drops a day and am now up to 12.  The 
problem is the Fe concentration stays at 0.1 ppm(LaMotte test kit.)  
 In addition to the Dupla drops  I add 6 of the Tetra Crypto tabs when 
I do the biweekly 30 gallon water change.  Is there something else I 
need to add to supply the iron?

Empirically, it seems that the plants are not getting something they 
need from the Dupla drops as they quit bubbling  (O2?) about 10 days 
after I switched from Kent fresh water plant food.  I find that if I 
augment the Dupla drops with some(0.5 teaspoon/every third day) 
Coralife marine iron suppliment I can keep the Fe level around the 0.5 
ppm range and the plants are bubbling as before.

Recently, I have noticed that Duplagan is being discussed.  I use Kent 
R/O Right and PH Buffer when I do a water change.  Which is about 30 
gal every other week.  From the ads I assumed the Duplagan was like 
Novaqua and I  didnít need it.  Would this be the source of iron I am 
missing?  Would I use the Duplagan in place of or in addition to the 
current stuff I add.

The vital statistics are tank 60x20x20 inches and has a ph controller 
set at approximately 6.8-6.9. Temp 75-77F. I have added 30 Dupla 
Laterite balls to the substrate.  6x40 watts of lights on for 12 hours 
a d

In advance thanks for your help.


I also would be interested in the group plant purchase.