after thinking on it, i'm not going to change my light period as things stand now. it's good advice, and I'll do it if my problem worsens - but as it is, twice weekly 25% water changes keep the tank looking good. the water's not *crystal* clear, but i'm not ashamed to have people over or anything.
it'll actually be interesting to keep all parameters the same and then hook up the co2 and see if that, by itself, stabilizes everything! in theory i should be good at that point. might be late next week, though - all my parts are shipped except fabco in florida. doesn't even look like they've processed or shipped my order, 3 days after placing it. hmmmm. they sure processed my credit card quick enough.