I think 25 mg of Foxy is way too much. Adding the acid on top of it ,first time trying it, is just stupid. You won´t even know what was the foxy and what was the acid!
And if your Foxy is uncut, 25 mg is just too much....
split the 25 mg into 2 piles. Take half one day and see what it´s all about with the foxy.
You will then know if it´s something you want to mix with acid. And you will still have a pretty good dose left to do that with.
Edit: but yeah, besides from that, I don´t see any problem in mixing acid and foxy. Pretty sure I have done it myself sometime.