swordplants with browning stems


I have a 55g with a ruffled  swordplant and a 10g with a regular swordplant 
that both have brown spots  in the stem at the base-. (Other regular 
swordplants in with the ruffled one look really good).  I removed the 
leaves. I know that swordplants need iron..could it be that I am using too 
little Flourish or too much? or something else wrong?
I bought the Seachem  tablets to put in the gravel by their roots to give 
them more nourishment, but thought I would ask first if it might be too much 
of something already such as iron.  Water quality: o ammonia, o nitrite, 20 
nitrate (water change last weekend), pH 7.2 and total water hardness 120. 
Lights are on a timer and set at 14 hrs. Hood and lights came with the tanks 
(perfecto and odell (55g)). The 55 gal lights are 3.5 months old  and the 10 
gal only about a month old . Oh, base is resin coated gravel; medium coarse 
size. Fish: angels, rainbows, corys, Sae's and one glass cleaner. There is 
some algae on the glass but the saes keep the plants and fake cave pretty 
clean of algae.

The rest of the plants (Anubias nana, water wisteria, hygrophilia polyspema, 
E. osiris, java fern)  look good (crypts ok), new growth and nice green. The 
swordplant in the 10 gal has 3 new baby plants growing at its base; but now 
has only short new leaves after I removed the  ones with browing stems..

SOOOO, what do you think might be the problem with the browning?
Thanks for your help,