Well, hydrogen peroxide does have its use. You do build up a little silver deposit on the inside of your container over time and that works like a third electrode and screws things up.
To fix this, wash the jar out with soap and water and rinse a couple times (tap water is fine). Then dump in maybe an ounce of hydrogen peroxide (just so its said, by itself - no added water), cap, shake for a couple minutes and dump out. It will remove ALL the silver deposits.
Now, rinse with tap water again 2-3 times to make sure you get all the hydrogen peroxide out, then rinse twice with a little distilled (add an ounce or two, cap and shake and dump) to get all the tap water out. You'll be fine.
I do this once every maybe 10 batches as a matter of course.
As far as getting hydrogen peroxide (ANY amount) in contact with colloidal silver, yeah, what cfnisbet said (wink). Even at 3% its a powerful oxidizer you don't want near Colloidal Silver.