Prism of Belief question

Can I use 2 at once if I have +3 to brutes and I want to add 1 + 3 to storm mages can I use 2 in this case or is it only limited to 1 (because you see the question is how does this limit work, is it only for one skill or can I also strengthen 2 skills)

The tooltip is insufficient in information and such questions arise.