Nitrite help?!

[rmschilling]

So, I checked my water recently and I noticed that my nitrite levels are really high (around 4.0??) but, my Axolotl doesn't seem to be showing any symptoms of stress, he's acting perfectly fine? I'm using test strips, so I honestly don't know how accurate these are (they're the marineland brand), I would use another brand of test strips to double check, but i'm all out, and I can't currently buy a drop test. Should I act quickly and take care of the nitrite just in case? If so, what do I need to do in order to get rid of the nitrite, and how can I prevent it from reaching such extreme levels.
I'm a bit confused too because I've been cleaning the leftovers from my Axolotl, as well as weekly water changes, so how did so much develop so quickly?
Please help, I really don't want my Axolotl to become sick