Ok, a lot of very questionable information going on in this tread.
#1 In order to get any plant to flourish, whether it be moss on a log or grass on the substrate, you need to give it what it wants to grow: light, nutrients, and carbon. This forum, more than others, seems to neglect the lattermost of these necessities. All the biomass needs to come from somewhere, and the CO2 dissolved in water generally isn't practical to support the necessary growth.
#2 I'm not sure where this iron-fetish has come from... The fact of the matter is that while iron is necessary for healthy growth, it is a secondary, if not tertiary need for the plant. You're not going to stunt growth by denying the plant iron, although you might get some chlorosis. Coupled with the fact that most carpeting plants are at best partial root feeds, and it makes even less sense.
#3 I've seen fine hairgrass carpets done in PFS with root tabs.
#4 WPG is crap. There are newer, better ways to describe lighting.
#5 I wouldn't advise 4x T5HO on a 40 breeder. 2xT5HOs on a 40 is a lot for non-excel, and you'll probably still be getting algae. I know that it sometimes works for some people (I hate you rookie....), but getting too much light for one's needs is one of the most common mistakes people make. Many of the bigger names in planted tanks actually recommend growing plants in medium light, but with supplemented CO2 and nutrients.
Mo' light, mo' problems.
#6 Please please PLEASE use more periods. I'm not going to flip about it, but it makes your posts difficult to understand at times.