Do test kits go bad?

I have seen these kits go bad.

In particular the Nitrate kit seems to be prone to becoming contaminated after time.

I could tell mine was bad from looking at the color of the crystal.  I was getting readdings that where really off.  I got some new test packets and retested, and the new ones worked great, and the readings where what I thought they would be.

If you are in doubt, have a friend come over, or borrow a kit and do double tests to compare values.

If the values you get are the same than I would say that the kits are still good.