API test kits

I finally got around to testing my tank for nitrate today. It read 5 ppm, which makes me doubt the accuracy of the test kit. Do these things expire? I feel like I've seen printed expiration dates on them before, but I looked for it and don't see anything on the packaging.

This tank has been fairly neglected. Last time I was away for a couple months the nitrate was above 100 when I got back. At that time the bottom of the tank was fairly well covered with big amazon sword plants. More recently I was away for 9 months, during which time the tank had maybe two water changes that were probably 30% or less, and the plants basically all died when the light bulbs burned out. I've changed effectively about 60% of the water, but apart from new lights stimulating algae I haven't done much to clean it up and I think the nitrate should be higher. I have added a bunch of new plants, but they've really only been there a couple days and probably haven't really rooted yet,

I'm trying to decide if I should be worrying about ordering a new test kit, or adding KNO3 to help out the poor starving plants.

How long ago was the test kit first opened?

By the way, new test kits are cheap. You can get something like 90 to 130 tests for under $10 delivered to your door.
http://www.ebay.com/...=item257eddf34d

They do expire, but that usually just makes them less accurate, as far as I know, not completely unusable. I guess it depends on how much accuracy you were looking for. I agree they are cheap enough though, if you have doubts.

Those tests should have a lot number on them somewhere. According to API, the last four digits are the date of manufacture, month and year, and they are supposed to be good for 3-4 years.