Frequency of Fe fertilization

I've recently started using Kent's iron fertilizer with Mg and K. the
instructions say to use 1-3 tsp per 30 gal at water change time. Since I
do a weekly water change for the 90 gal tank, I should use 3-9 tsp once
every 7 days. Instead of doing so, I've been adding daily dosages of 1 tsp
per day. I thought this would provide a more steady supply of nutrients.
Is this ok, or did I miss something completely? I was also concerned that
my use of a de-chlorine chemical at water change time would effectively
neuralize the trace elements.

I know that Dupla is a proponent of the daily Fe regime. How come other
brands recommand weekly or bi-weekly Fe feeding with water change? 
How long do the nutrients remain available to my plants in the aquarium 
water anyway?

 John Y. Ching (jyching at watnow_uwaterloo.ca)    |
 Pattern Analysis and Machine Intelligence Lab	| 
 Department of Systems Design Engineering      	| 
 University of Waterloo, Canada            	|