I feel like an idiot, didn't even notice that above the label on mine.... I would do one more change and see if you get more of a orange color. So they should last about 4 years.
oh and those aren't worms in Knotheads pic.....bubbles, from filter return. water was pretty low, it was the only way I could get him to co-operate for me to get pics of him.
Don't need to shake it. Lol nitrates are the worst to do. Also get a pic in a neutral lighting or white lighting if you can, the lighting the last few pics has been warm which won't show the color as correctly.