I got an iron test kit today and found out that I do not have any amounts of
traceable iron in my 48 gal. planted tank. I've added some liquid fertilizer
that is iron-enriched. I've tested the water again in a hour and there is
about .35 to .4 mg/L now...which I've heard was good.

Is liquid fertilizer a good way to supplement iron to a system? How long
will it be till I usually have to add more in? (Or I can continue testing
every 3-4 days for chelated iron levels)

thanx!