I'm dosing with Fe because it's all being used, and I'm trying to give my
plants a leg up on the algae. Is that wrong?

In order of importance, fix light levels, then CO2, NO3/PO4/K+ then finally
play around with traces. Traces are just that trace and have little effect
on anything unless the big nutrients, CO2 NO3/PO4/K are taken care of.

I've actually stepped back my lighting from 220 watts but am adding CO2

Can you get somewhere in between 220 and 110? Around 150 would be great,
3 55W PCFs maybe. 220W might be a little challenging, but it's very
possible to get things balanced.

because it helps lower my Ph and, according to the "Determination of CO2
Content in Aquarium Water" table I'm using, with ph of 7.5 and Kh of oh,
say, 15, I expect the CO2 content to be about 11 mg per quart which would
be
at the low end of desirable, or do I have that muddled?

At a KH of 15 I would be shooting for a pH of 7.2... neutral 7 might be a
little too far, you may see some fish getting stressed. Ideally you want
25-30ppm if you can, I don't care what kind of lighting you have.

I'm still getting around the idea of carbonate hardness which I had rather
thought in my muddled way to have been subject to "manipulation" as
opposed
to Gh aka permanent hardness which is, well, permanent. At any rate, I'm
using coarse gravel out of a bag from Petco, brand and chemical
composition
long since forgotten, but the standard stuff.

All these terms stink, and I hate that aquarium literature uses them. "dKH"
is really alkalinity, a measure of the total amount of base present in your
water. "General Hardness" is the amount of Ca++ and Mg++ in your water
(actually includes other divalent cations too, but they are not very
common).

Give http://www.sfbaaps.com/reference/barr_02_01.shtml a read. You may find
you need to bring the KH down by using an RO system over the long haul, 15
dKH is a lot. Stick with vallisneria and egeria densa, and the true
aquatics if you water is this basic, also any plants that grow near Lake
Tang would be pretty good... a lot of the amazon/soft water marsh plants may
grow more slowly than usual.

Cheers,
Jeff Ludwig