Iron oxide from iron filings

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I've been working on making my own iron oxide. I got a lot of iron filings from a local ironworker. I put them in some warm water and pumped air into it with an aquarium pump (for oxygen). After a few days, I stirred the whole thing up.. raising up the black iron oxide particles. (The filing are too heavy and they sink.) Then I separated the resulting black liquid, and filtered out the iron oxide. I got about 2 spoonfuls.

So I'm thinking of getting it done much faster with pure oxygen formed by electrolysis. Now how can I do this efficiently? My main problem is figuring out what to add to the water to make it conductive.. I don't want to use salt, because I'll get a lot of chlorine and not a lot of oxygen. I tried sulphuric acid, but the carbon on the oxygen side corrodes like hell, and throws a lot of carbon particles all over the place. I tried both pencil lead, and carbon rods from batteries. I'm wondering, is that because of the SO4 ions, or does the oxygen destroy the carbon? In any case, does anyone have any suggestions? Would sulphuric acid affect the iron in any way?

By the way, I've tried searching the forums, but it doesn't work right.. It seems to find almost every thread, no matter what I type in there.