Hi Amy,
It's only the Pelikan blue-black which has an iron gall component, in fact the only IG fountain pen ink which isn't BB is Scabiosa so far as I'm aware. (I made my head swim reading up on the chemistry of all this last night and probably understood one word in ten, but apparently it's the "iron-bluing" tannins which make the ink permanent, so maybe that's why). The benefit of adding lemon juice is that the ink will strike into the paper surface more effectively, but it'll doubtless make it more corrosive if anything. But if you're going through a nib a day, that sounds more like fair wear and tear to me than corrosion, especially if you're working on Spencerian capitals.
I have another tentative suggestion for you, and I'm fairly confident that Schin will agree with me on this one. If you buy the Walker Copperplate Ink (and it's every bit as good as people say), also buy a bottle or two of Roberson's Penman Classical Transparent and try that for practice. It's a non waterproof ink which flows in much the same way as an iron gall, but won't eat nibs. Schin got one of the reddish colours and liked it; ditto for me with the black. Scribblers stock both Walker's and Roberson ... the only other place to get the former is Penman Direct but ordering is less straightforward.
