beware of too much iron

I have been using PMDD's in a 42g for about six months now. The
results have been terrific. Algae virtually disappeared, and plant
growth has been wonderful. As an experiment, I decided to tweak the PMDD
formula with an extra teaspoonful of chelated iron. The
result....nothing for about two weeks. Then, the plant growth in the 42g
slowed dramatically, and soon algae started to reappear. Limnophila
Sessiflora and Gymnocoronis Spilanthoides, which were being trimmed
weekly, virtually stopped growing.
Hygrophila Polysperma var. rosaenervae developed holes in the older
leaves and stopped growing. A green thread algae which wasn't noticeable
before returned with vigor, rapidly becoming a problem. After 2 more
weeks Hydrocotyle Leucocephala showed distinct areas of yellowing
between the veins of the leaves. I decided that enough was enough, and
returned to the original PMDD formula, as well as doing increased water
changes. Gradually the algae started to decline as the growth of the
plants returned to normal.
    During this time I monitored the NO3, PO4, and Fe levels. There was
no noticeable change from what had been normal. The NO3 and PO4 tests
are from SeaChem, and the Fe test is from Red Sea. The Fe level measures
0.1 on the Red Sea test constantly. With the increased Fe dosing, the
test never changed a bit. Even when it appeared that Fe levels had risen
to the point that they were interfering with the uptake of other
nutrients, my test kit still indicated 0.1 . 
    I would like to repeat this experiment with perhaps a Lamotte test
For now though, I will stick to the original PMDD formula and feel
pretty good about the amount of Fe in the trace element mix that I am
    Conclusions? None, but I would be cautious about adding too much
iron to my plant tank. Also, I'm not a big fan of the Red Sea iron test
    Question.....When my plant growth slowed down, why didn't I see a
rise in the NO3 and PO4 levels? Could this be a test kit problem?
    I would also like to see a comparison of some test kits done. I hate
wasting money.
Perhaps this could be an article for the Aquatic Gardener, or could be
posted to the Krib. Perhaps some of the wealthier (or should I say, less
financially challenged) members of the Digest would care to undertake

Pat Bowerman in Northwest Arkansas, where the fall colors are at their
beautiful peak