Old vs New Test Kits?

[ShadowStryder]

I have always read that you should not use a test kit that is older than one year old. I have had the same test kit for 15 years now, (shows how frequently I test my waters) But after continuously hearing that you shouldn't use one that old I figured what the hay I will pick one up today. It is a API liquid Master Test Kit as is the old one that I have.
So just out of curiosity I tested my water with both test kits. Low and behold the readings are literally identical. I did this test 3 times just to ease my conscious that I didn't screw it up. Nope all three times they were the same.
So my question is really just being thrown out there to anyone in general or maybe someone who truly knows the answer:

Where did the practice that old test kits aren't accurate start. Is it a manufacturer started rumor to keep up sales or is there a study that states this as fact? .

 

[spotfin]

Good question. I have an API ammonia test kit that is at least 15 years old as well. It tests the same as the one that is 2-3 years old. Same for a pH test.

 

[HULON]

LOL !!!! Of course Api started that rumor and i have had the same experiance....I should add that the chemicals go stale eventually and probably don't work as well at some time but i am sure this takes a long time...

 

[DB junkie]

I had 40 PPM difference in Nitrate from my first test kit to a new one.... Prolly 5 years old. Everything else but Nitrate tested very similar.

Although I am starting to question Nitrite.... I've never seen anything but 0 ever. I think the test kit might be baby blue food coloring.

No different then expiration dates on food. Bunch of liars. lol