I think I've got the swing of this. After six weeks, the tank appears to be established, although I'm still having problems with water hardness and low pH. This morning, Nathan at Nippon Goldfish gave me some pointers for correcting the chemistry. If it works, I'll stop fussing over such things and start adding little fishies.

Here's what I learned talking with Nathan:

His beautiful Amano tank? He doesn't bother testing CO2 ppm. Instead, he uses the far less exact but much easier method of tweaking CO2 bubble count. He thinks I'm probably injecting too much CO2, and suggests I try about one bubble every four seconds, which would be half to two-thirds of what I try to maintain. Slightly less CO2 should prevent the tank water from acidifying so radically.

Nathan says carbonate hardness is, after lighting, the one thing to get under control. Once that is stable at 2-3, then my pH troubles should go away.

I bought a Hagen Fe test kit, which -- finally -- allows me to collect accurate chelated iron readings. I was happy to see that my tank water registers in the desirable zone, a zone the Red Sea Fe reagents apparently weren't able to register.

Yesterday, I ordered two additional test kits (CO2 and pH), by LaMotte, maker of high-end aquarium test products.