That was one of my thinking. Not that it's old, but maybe not good (I bought it 3 weeks ago). I bought another ammonia test this am and still nothing.

You're running into the same issue I had with my first planted tank. Cycling is very hard to notice when the plants are greatly masking the process. Your plants are kinda like algae... they suck up all that waste matter in an attempt to get nutrients. Of course, they don't use the ammonia and nitrate, but it ends up in their biomass anyway. Plants are weird lifeforms, they often just pack nasty chemcials in themselves without a care. xD

Thus, all that ammonia and nitrate is still IN the tank, just not in the water as much, so its harder for the tests to pick up. The tank will still be cycling though. Personally, I'd suggest adding a few more fish. Tetras are sooo small that the waste they make is tiny compared to the volume of water.

About "Cycle", I've never used it. I'm personally against using chemicals in my water as much as possible. Keeping the tank as natural as possible is always a good goal.

As far as I know, plants will stuff anything thats in the water into their biomass. Its a natural part of how they grow, as far as I know. I could be wrong however. I am certain that they absorb nitrate though.

And, it's possible to have both nitrate and ammonia in the tank. ;) The bacteria in your tank might not be established enough to process the ammonia at a rate fast enough to keep up with you're tank, while still being established enough to produce nitrate. The other thing might be a sudden amount of decaying matter. Are you trimming your plants of their dead leaves? Are you fishing out the floating ones with a net? The decomposing plant matter is just like decomposing fish or food, it adds ammonia too!

I'm thinking that your testing equipment is on the fritz. You can't "skip" ammonia and nitrate. They need to exist in the tank for the bacteria to grow. Given, your plants are likely masking this whole process, but still, you should take a LOT of caution before you put the rest of your planned fish in there.

My advice at this point is take it to your closest fish store. They often do free water testing, or do it for practically no charge. They should be using up-to-date kits, and are likely (though not always) more experienced in reading/using the testing kits. If their numbers are matching yours, then you may have just gotten lucky. xD

its very possible to miss a nitrite or ammo reading if you're cycled properly, because these quickly get converted to nitrate. How often have u been water changing and how much?