i'm unfamiliar with 'poisoncraft', but you may want to ask your DM his opinion on it. open and nonconfrontational talking can work wonders for a campaign. if he thinks it's getting a little much and making the other players feel useless, maybe talk about scaling back some of the powers to the realms where they're more in-line with the rest of the party (whether that means advancing them or lowering you is a choice the two of you should decide upon)
while there's a lot at CR9 that's outright immune to poison, a DC of 30 is truly nasty even for things that rely on a superior fortitude save. for example, a frost giant's fortitude save is +14, which could be bumped upwards a few with minimal items and perhaps a minor stat revision. even still, there's a fairly good chance that he'll fail such lethal DCs for the poisons you're cranking out.
while this might be cool for a few battles, it may get tedious and boring, or worse, your DM might react poorly and just start throwing out things that are either immune to poison outright, or somehow have +25 to their fortitude saves - either option cripples your character build.