It's been quite a few years since that chemistry class I never took, so if
someone could give me a hand here, I'd be grateful.

I've got a 75-gallon standard tank with 110 watts of lighting. The tank has
lots of wood in it and is moderately to heavily planted and I'm injecting
CO2 through a powerhead and also with a diffuser next to the filter output.
I have a pretty heavy fish load for a planted tank, but my maintenance is
impeccable (imho).

Forty-eight hours after it's weekly 20% water change and adding double the
recommended dosage of trace iron, my stats a

Ph.............7.4-7.5
Nitrate.......not measurable
Nitrite........ 0.5 ppm
Gh.............3º
Kh............. 12º
Fe............. not measurable

I say the carbonate hardness is not measurable because after 12 drops it
just turns the same colour as the test liquid.

My water comes from a well which feeds into a water softener in the
basement. There is no practical way to bypass the water softener.

My specific concern is algae, and I've got a small, tolerable amount every
kind I've ever heard of and then some. The plants are all doing "OK" but
I'm afraid that things might be starting to slip away from me, despite two
2" plecos, a dozen ottocats and a host of snails of every race, creed and
colour.

Paradoxically (perhaps), the Red-spot Ozelot and the Hygro Corymbosa are
vividly red and thriving, so I'm thinking that that's where all my iron
went, although I can't explain how or why. I've been totally unable to get
water sprite established (the gouramis may be a contributing factor there)
and the crypts aren't spreading. The fish are all fine.

SO... Do I lower the Ph and Kh and, if so, how? And how do I keep them down?
If anyone has product recommendations I would be grateful, preferably online
in the U.S., as there are no intelligent life-forms in my local shops.