Added Siporax to mine a few days ago, and was going to wait a good month before expecting anything amazing, as far as I could tell, it's just very porous to host tank bacteria as live rock would. Expecting roughly the same period as anew tank then for it to start doing it's do.
Interestingly too, I chose to add it to supplement the NoPox, I read a fair bit around it before hand and both AAC and RedSeaKev mention that the two compliment each other nicely, the carbon dosing feeds the bacteria you want grow on the Siporax. As far as NoPox is concerned, the Siporax gives more solid surface area for the bacteria to settle on

That was my take on it anyway.
Are you finding your Tux is managing to keep on top of the GHA? I added mine from the other tank and ever since he's raced (relatively) around the tank but seems to be struggling to keep on top of it. I was tempted to get another, my LFS tends to get the pretty purple ones, so fancied getting him a mate to help him out.
@
warby - Am I kidding myself that giving NoPox time to get established is going to start getting on top of phosphate? Would you recommend an additional method for phosphate regardless?