safe iron levels

	I have a 55g tank with fine gravel substrate and dupla laterite. 
The tank is pretty well planted with a variety of echinodorus,
valiseneria, and hygrophila species plants.  I have been using the 24
drops and the dupla tablets (at water changes) but have discontinued using
them in attempt to lower the Fe level.  According to my LaMotte kit, the
iron is about 0.3-0.35 ppm The fish, 2 cobalt discus, are breathing rather
heavily (iron associated?).  In any case, what is a "safe"/"ideal" Fe
concentrations in a fish/plant tank?  Is it the laterite that keeps the
iron at this level?  My tap has less than 0.05ppm Fe, and I change about
7-10 gallons weekly.  The tank is filtered by an Aquaclear 300 with double
sponge and no carbon or any other media.  Ph 6.6, temp 86F, light 80W
(triton/vita).  Thanks for any help on this matter.   Tom
(misiak at fsu_fsufay.edu)