Thank you for the answers,
Powder looks like a cheap and good solution, i just didn't want to bother with conservators, I read everywhere that self made gum solution with powder will not last on shelf if you don't add some chemicals in it, so i was thinking it was nice to think to get some ready made solution.
I am glad to hear that I could use that food gum powder, This would be OK ? here it's called "E 414" : (sorry german):
where do you get the additives ? if i am correct : Thymol and isopropyl alcohol, I am in Austria, and it's quite hard to find that stuff if you don't know where to search...