New tank, strange water readings

[elmonty]

I have a new 29 gal tank. It was filled last Monday. Over the next few days, I did a couple of water tests and the results were fairly consistent:

pH=8.0
KH went from 4 to 3
GH went from 7 to 9
Ammonia=0
NO2=0
NO3=0

Thursday night, I put in two gold gouramis, two paradise fish, and some Anacharis plants. Friday morning I did a water test. I expected to see some ammonia, but I was surprised with the results:

pH=7.5
KH=3
GH=8
Ammonia=0
NO2=0.3
NO3=12.5

These are readings I would expect from a fully cycled tank. I have not added any chemicals other than AquaSafe dechlorinator -- and that was when I filled the tank on Monday. Why would I get these readings?

This morning (Saturday), I got the same test results:

pH=7.5
Ammonia=0
NO2=0.3
NO3=12.5
(GH and KH not tested)

Any ideas?

[Hound]

I'd say keep testing. If you didn't sterilize the plants I guess it might be possible they had enough bacteria on them for the fish you have, but that would just be a complete shot in the dark.

[elmonty]

No, I didn't sterilize the plants. Was I supposed to? Wouldn't that kill them? Besides, I was hoping they'd have some bacteria, but they weren't in a tank with fish at the LFS.

[Jay]

I’m suspicious of a 0 ammonia while nitrite and nitrate are registering.
What is your test kit?

[elmonty]

I'm using the TetraLab master kit and the Tetra NO3 kit.

[Hound]

My basic guess would be that the plants had some bacteria on them that jump started your bacterial cycle. Most people do a basic type sterilization on new plants to remove possible hitchhikers such as snail eggs.