You need to add very small amount of your glutaraldehye stock solution to your chitosan solution, can you see how to get from 25 % to 0.1 %? At any rate, you will slightly dilute your 1% stock in the process, but that might not be a significant for your application, I'm just being absolutely correct.
P.S. never forget to include the placeholder zero when you write a concentration, especially when you write it on the bottle by hand, a decimal by itself might not be noticed. It happened to me, and it was all my fault when they made the mistake on my day off, and assumed I meant 1 M, instead 0.1M.